Dark Angels
The Dark Angels were the first Space Marine Legion to be formed by the Emprah. Their Primarch was Lion El'Jonson. As a result, the Dark Angels are totally gay, (Heresy!) their Primarch happening to apparently be named after a homosexual poet.
The original Dark Angels had black armour, back in the days of the Corvus pattern helmets. Modern Dark Angels instead use a dark green colour, except for the Deathwing company, which is composed entirely of bone-white Terminators. They were introduced in the Deathwing expansion to 1st edition Space Hulk with a spiffy background story by Bill King.
It is a well known fact that Lion El'Jonson threw Leman Russ, the dog faced primarch of the Space wolves through a wall after the Dark Angels defeated Tyrant Durath, a heretic that had insulted Leman. Russ was strucked unconscious and suffered a case of bad headache.
History of the Dark Angels
The Dark Angels were the first Space Marine Legion to be formed by the Emprah. Due to a slight mutation in their geneseed, they had a slight predisposition to be emo, but other than that, they were cool. The Dark Angels killed lots of Orks and other Xenos Scum for great justice and were the most successful Space Marine Legion during the early years of the great crusade, though their critics pointed out that the Dark Angels, being the First Legion, got a head start. (note to webmaster: they might have been the 1st legion but Horus Lupercal was the first primarch to be discovered and as such he got a head start not them, as well as his legion being the most succesful hence why he was appointed Warmaster not Johnson)
However, one dark day, they were betrayed by Lex Luthor, who brainwashed the marines garrisoning the Dark Angel's homeworld of Caliban, causing them to turn to Chaos and become the Fallen. Crazy things happened, and the next thing you know, Lion El'Jonson'S missing, Luther's insane, and Caliban is a friggin' field of debris. Oh,and the loyal Dark Angels painted their armor green. This rather stressing turn of events caused one Dark Angel to comment, "I hate Mondays."
Ever since that fateful day ten thousand years ago, the Dark Angels have striven to prove to the Emprah and their Primarch that they are still cool guys to hang around with, despite their earlier Heresy. Therefore, they have acquired toys like Plasma Cannon armed Jetbikes,Terminators that count as scoring units, and a mini-Gitmo in an asteroid to torture the Fallen, in order to prove that they are still made of awesome sauce and epic win, and to attempt to disprove the rumor that that they are flaming homosexuals,however, having xeno pokemons instead of servitors make a probe they are still being extremely homo.