Presented for your enjoyment, 
the following is a compilation and summary
written in my own words and mostly from memory of the history 
of the Blood Angels as presented in the 2nd Edition Angels of Death Codex,
3rd edition codex, and subsequent White Dwarf articles 
of the history of the Blood Angels.
~ Brother Edward

Introduction

Blood Angels are one of the most famous chapters of the Adeptus Astartes. 
They are well known for their aggressive assaults and a thirst for battle which seems to border on insanity, yet few outsiders know many details beyond these outward appearances. In fact the Chapter has a very rich history, filled with traditions of loyalty and courage, and some unique problems which challenge their ranks every day. What you are about to learn is known only to a very few....

The Primarchs and the First Founding

Blood Angels are one of the First Founding Chapters, before we can discuss this we should review the history of the creation of the Primarchs and the First Founding. Originally the Emperor of Mankind created twenty Primarchs (genetically modified "super humans") each of whom had their own special qualities to aid in protecting humanity in it's struggle for survival. Each of these Primarchs would lead their own Space Marines Legion. Each Space Marine with these Legions was created using genetic material from the Primarch - giving each Space Marine Legion certain unique abilities and attributes beyond the amazing physical and mental abilities which all of them possessed. The Space Marine Legions created from the Primarchs in this fashion are known as marines of the First Founding. 

The Great Crusade

The purpose of the Primarchs and the Space Marine Legions is that they would comprise a totally loyal warrior caste for the Emperor. These super warriors would know no fear, and have no concept of self except that they must serve the Emperor and protect mankind. Armed with these Legions (the Legions Astartes) the Emperor and the Primarchs would battle the enemies of mankind in the Great Crusade to renew contact with human settlements long lost after the Dark Age of Technology. This vision of a cosmically expanding humanity under the protection and guidance of the Primarchs was profound, so much so that evil forces acted to intervene.

Immediately after the creation of the Primarchs (while they were all still infants) unknown powers (presumed to be Chaos powers) attempted to destroy the Primarchs, though failing in this, the Primarchs were scattered throughout the galaxy - their exact locations unknown even to the Emperor. However the Emperor still had the materials needed to create the Space Marine Legions, and having created them he began the Great Crusade to reunite humanity with all of it's lost elements, and to find the Primarchs. Scattered across the universe as they were, each of these infant Primarchs were still very nearly invulnerable - they possessed supernatural toughness, strength and intelligence well beyond the scope of mortal men. Each Primarch ended up on different worlds, each of these worlds was physically harsh, the indigenous culture primitive. Each infant Primarch faced their own unusual challenges, but each rapidly grew to adulthood, gaining the respect of their local populations in the process and in many cases bringing order to the entire planet. As the Emperor traveled the universe he was seemingly drawn to the locations of each of his lost Primarchs, and it is said that in one way or another all of them recognized the Emperor to some extent on sight. Ultimately each Primarch joined the Emperor's Great Crusade, and each was given command of their own Space Marine Legion.

Sanguinius

One infant Primarch appeared on the radiation blighted deathworld known as Baal Secundus. Civilization on Baal Secundus was organized into tribes, the human inhabitants of Baal struggled constantly for survival against tribes of other humans terribly mutated by the radiation which threatened them all. Into harsh world fell one of the infant Primarchs. Discovered by a human tribe in an area so poisoned by radiation that it should have killed the child outright, the infant Primarch was taken in by one of the tribes of Baal (a tribe known collectively as "The Folk of the Pure Blood" or more simply "The Blood"). Despite having a tiny pair of angelic wings the child appeared as normal in every other physical respect, more than normal the child was beautiful by every standard. Though many argued that the infant be put to death due to his obvious mutation, ultimately the decision was made to take the child in, care for it, and raise it as one of their own. 

The infant Primarch grew much more rapidly than any normal child. In three weeks he was as large ar e child of three years, and after one year his appearance was that of a young man in his prime. Already he could walk unprotected into lethally radioactive areas, and his wings had grown to carry him high into the skies above the blighted lands. He rapidly mastered all aspects of his education, and quickly became the better of all who had taught him the ways of combat and war. Sanguinius' compassion and love for his people was without end, but so too was his anger when his tribe was threatened. The Folk of the Pure Blood kept no written records at the time (their history was kept through an oral tradition) but tales from that time recount several instances where Sanguinius fell upon the enemy with an unbridled rage the likes of which no one had ever seen, coupled with his incomparable strength and martial skills Sanguinius was completely unstoppable on the battlefield.  Ultimately Sanguinius rose to lead the Folk of the Blood, and bring order and prosperity to Baal Secundus.

The Blood Angels

Ultimately the day came when the Emperor's Great Crusade brought him to Baal Secundus. It is said that Sanguinius recognized his Emperor immediately, and knelt in fealty at their first meeting. Sanguinius was introduced to his Legion of Space Marines and the Blood Angels were born.

Once Sanguinius joined the Emperor's Great Crusade he and his Blood Angels distinguished themselves with their loyalty and their martial skills. During the Horus Heresy when the Warmaster Horus (once the Emperor's favored Primarch but now corrupted utterly by Chaos) turned fully half of the Primarchs and their Space Marine Legions against the Emperor Sanguinius and his Blood Angels remained loyal. Indeed Sanguinius and his Blood Angels were one of only three Space Marine Legions to be present there on Tera side by side with the Emperor defending the Emperor's Palace from the full might of Horus' assembled traitor legions, traitor titan legions and the daemons which Chaos had sent to aide them. The Blood Angels distinguished themselves in the defense of the Eternity Gate Spaceport, and Imperial histories record Sanguinius' legendary battle with a gigantic Bloodthirster in the defense of the Ultimate Gate of the Emperor's Palace. With the outer walls having been overrun the defenders were forced to take the battle inside the Emperor's Palace itself. Sanguinius alone held off the hordes of chaos as the last of his wounded men were carried through the Ultimate Gate. The great armored doors were just about to close when from the throng of chaos warriors a Bloodthirster of enormous size rose to challenge Sanguinius, and though already having fought for quite some time and bearing multiple wounds Sanguinius rose to the challenge and singlehandedly defeated the archdaemon in a colossal battle, and with a halo oof power playing around his head Sanguinius threw the broken body back into the crowd of onlooking chaos warriors who beat their chests and ripped out their hair in dismay as the Ultimate Gate was finally shut.  

Soon thereafter the Emperor made the decision to take the fight directly to Horus and settle the conflict face to face. The Emperor along with his closest personal guards, Sanguinius and a number of his Blood Angels (and Rogal Dorn with a contingent of Imperial Fists) all teleported aboard the bridge of Horus' battle barge to end this maddness once and for all. However the warping effect of chaos had not only turned Horus' soul, but it had in a very tangible way warped his body, his flagship, indeed all who served the chaos warmaster had been horribly twisted into shapes reflecting their newly corrupted evil purposes. When the Emperor and his assault party teleported aboard the Warmaster's vessel the entire assault party appeared not on the bridge of the ship as they had intended, but rather scattered individually at random locations throughout the chaos warmaster's flagship. So horribly twisted and perverse had the ship become physically that many veterans of centuries of warfare went immediately insane from what they saw when they teleported aboard this ship. Some of the Emperor's finest warriros even died outright from the shock of the experience, but the Emperor, Sanguinius and a handful of the assault party endured the unendurable, and continued on with their assault even sepparated as they were. Sanguinius however was the first to find himself face to face with the Warmaster. Horus tried to tempt Sanguinius to forswear the Emperor and join with the forces of Chaos, but Sanguinius utterly rejected the notion, and chose to assault Horus with all of his might. Despite Sanguinius' godlike skill, strength and determination, Sanguinius was no match for the Warmaster at the height of his power. With the power of all the chaos gods coursing through him Horus slew Sanguinius.  Moments later the Emperor came into this room, and seeing the body of Sanguinius dead on the floor the Emperor of Mankind joined in the final battle with his once close friend now arch enemy Horus the Warmaster. In a battle with no parallel, energies which could have split a planet were unleashed between the two - one a champion of good, the other the champion for all that was evil. In the end Horus lay dead, and the Emperor's own body was shattered. The death of the chaos warmaster was felt across Tera and across space, without the warmaster to channel the vast energies of chaos the armies of chaos immediately began to lose their initiative and lose their organization. Across the planet and in space the forces of chaos and began to fall back. It was Rogal Dorn who found the Emperor barely alive, he and the survivors of the assault party teleported back to the Emperor's Palace with their dead and wounded, taking the Emperor to a place of safety where he was placed into an ancient device to preserve his life indefinitely, the device now commonly referred to as the Golden Throne. The Blood Angels would now continue the fight against the retreating forces of chaos without their Primarch.

By the time of Sanguinius' death the Blood Angels had already earned a reputation for loyalty, and ferocity in battle, but this was just the beginning. Almost immediately after Sanguinius' death a change fell over the Legion. While it was well known that Sanguinius had been an an amazingly powerful psyker, especially gifted with the ability of prophesy, no one had forseen the powerful effect that the Primarch's death would have on his Space Marines. In the days and weeks following Sanguinius' death a number of Blood Angels became overwhelmed with visions of battle, images of twisted leering chaos faces, impressions of fighting so real that these hardened warriors were unalbe to distinguish reality from illusion. In short order a pattern emerged, these Blood Angels were having mental glimpses of the final days of Sanguinius. It has since been surmised that Sanguinius' psychic deathcry had been so powerful that it was sometimes possible for those who had his geneseed to glimpse and experience some of what Sanguinius endured in those last days of fighting and especially the time aboard the Warmaster's battle barge. Over time it became apparent that many Blood Angels were experiencing something of these visions, but for some the visions and experiences were too overwhelming, they could not distinguish halucination from reality, and it was discovered that ultimately the experience would prove fatal, but not before taking the sanity of the Blood Angel so overcome. The last days of life for a space marine in this condition were not pleasant - fighting imaginary opponents, feeling the real pain of the wounds which Sanguinius endured, seeing the sanity blasting nightmarish images of chaos corruption from the warmaster's battle barge, and ultimately dying from the shock of reliving Sanguinius' own death. 

A decision was made to identify Blood Angels who were beginning to show serious symptoms of this condition, and form them into a special unit called the Death Company. This unit would be led by Chaplains, and Emperor willing these Blood Angels would be able to die in service to the Emperor rather than lose their sanity and die as madmen. Those admitted to the Death Company have their armor painted black, and their armor is adorned with large red crosses which symbolize the many wounds which Sanguinius endured in his final days of service to the Emperor. This unit quickly earned a fearsome reputation, for not only were these marines seeing and feeling something of their Primarch's experiences in the final days of the Horus Heresy, each of these marines also experienced a small portion of their Primarch's strength, toughness, and martial ability as well. The ferocity of the Death Company in battle was unmatched, and their altered state of mind allowed them to continue fighting despite suffering wounds which would kill lesser men outright. The tradition of the Death Company continues in the Blood Angels to this day, and watching over them is the duty of Chaplains within the Blood Angels (and their successor chapters).

The Blood Angels also grew to incorporate a new position within their ranks - that of the Sanguinary High Priest. To understand the importance of the Sanguinary High Priest one must know more about how Blood Angels are created. Unlike the process used to create most space marines (years of surgery, augmentation, geneseed implantation followed by more surgeries and chemical regimines) Blood Angels follow a unique process wherein the aspirant is given a chalice by a Sanguinary High Priest, the Aspirant is told the Chalice contains the blood of their Primarch and is instructed to drink. Having partaken of the contents of the Chalice the aspirant soon falls into a deep slumber. The geneseed is then implanted, and the aspirant is placed within a special sarcophagus which will facilitate the entire transformation from normal human to fully developed Space Marine within the span of a single year. The not widely understood truth is that while it is a simple matter to implant a geneseed into a body, it is more difficult to stimulate the geneseed to begin functioning so that it begins to affect the body it is in. In the beginning Space Marines were injected with a tiny bit of their Primarch's blood to activate the geneseed to begin the process of transforming the aspirant into a space marine. However with the death of Sanguinius this process clearly could no longer continue in this manner - enter the Sanguinary High Priests. Chosen from the ranks of the most capable Blood Angel veterans, Sanguinary High Priests are known as "The Chosen of Sanguinius" - they embody the best attributes of Blood Angels. Sanguinary High Priests are actually privileged to partake of a small bit of Sanguinius' blood (stored in the Blood Angel's home fortress), then it is the combined blood of all the Sanguinary Priests which the aspirants consume in order to awaken the geneseed in their body - thus beginning their metamorphosis into a Blood Angel. The process of undergoing the entire transformation in only one year is very unusual among the many varried and highly ritualistic methods of creating space marines, and it is rumored that many Blood Angels often choose to rest (when afforded the opportunity) within the Sarcophagus in which they were created - some believe this has something of a purifying effect on the space marine, and perhaps this explains to some extent the long lifetime of Blood Angels. All space marines have a lifespan much greater than normal humans, space marines may see several centuries of combat, Blood Angels however are especially long lived - even for space marines, many Blood Angels live to be over a thousand and still fight on with strength and stamina greater than that of younger space marines. The unusually long lifetme of Blood Angels also gives rise to an unusual pursuit - Blood Angels as a whole seem to appreciate fine art. There are many reasons this may be so, but what is clear is that Blood Angels often refine art (which reflects their service and duty to the Emperor of course) over the long span of their lifetimes - this explains why Blood Angel banners, heraldry and armor are among the most decorative in all the Imperium.

After the Horus Heresy  (in an effort to avoid another widespread space marine uprising) the Space Marine Legions were broken up into smaller units called Chapters. Each Legion had been composed of around ten thousand space marines, whereas each chapter had only one thousand space marines. The creation of the space marine chapters is known as the Second Founding. Only one chapter retained the name "Blood Angels", the newly formed successor chapters (chapters made from the ranks of the Blood Angels) created new names like the Angels Encarmine , the Angels Vermillion, The Angels Sanguine, the Blood Drinkers, the Flesh Tearers and more. 

Today the Blood Angels are still famous for their ferocity in close combat. Over the millennia they have refined their skills, their very name now name is nearly synonymous with assault tactics and in some cases an unusual thirst for blood. Indeed they are acknowledged by all who know them as being one of the most capable assault armies in the Imperium, and they are regarded by many with awe and fear in equal parts.  Despite the wild rumors of their detractors, the Blood Angels are still utterly devoted to their Emperor and the Imperium. They can be found in the thick of the bloodiest fighting, and in many instances mere rumors of their approach can restore order in some restless systems.

Every day Blood Angels strive to live up to the standards of martial prowess and selfless sacrifice as set by their Primarch Sanguinius. Every day the Sanguinary High Priests continue the traditions which have maintained their chapter in these ten thouand years that Sanguinius has been gone. Every day Blood Angels see, feel, and sense psychic glimpses of the final days of Sanguinius. And every day for some few Blood Angels (especially on the eve of a great battle) these psychic impressions become all too vivid, all too real, their minds are yanked back in time to another place, another time, and when the Chaplains see that all too familiar distant look they know it is time to add another Blood Angel to the Death Company. With the spirit of Sanguinius watching over them hopefully the Chaplains can lead them to honorable death in the service of the Emperor, just as their noble Primarch Sanguinius died while fighting to serve the Emperor and mankind.

For further insights into the rich history of the Blood Angel you 
should try to obtain the following references:

The 2nd edition "Angels of Death" codex.

 US White Dwarf 260 for the Index Astartes Article 
in US White Dwarf 260 covers the Blood Angels in great detail, 
revealing yet more secrets which I've not covered here!

US White Dwarf issue 267 which discusses the Black Legion and 
the Horus Heresy also has yet more information on the Blood Angels, particularly 
their role in the Horus Heresy and the defense of the Emperor's Palace!

~ Brother Edward

Lord Dante - Current Chapter Master of the Blood Angels