Lion El'Jonson
The Lion was, aswell with all other Primarchs, made on Terra, but sucked into the Warp by the Chaos Gods.
Lion El'Jonson crashed on the Death World of Caliban. He was found and raised by Luther, The Lion's second in command before the Horus Heresy. Lion was quickly persuaded to join the Order of Knights, which he did. It didn't take him very long to become the Supreme Grand Master of the Order, having eradicated one or more of the Death World's Great Beasts.
Jonson was found by one of the forward scouts of, ironically enough, the Dark Angels who told the Emperor that he found one of the Primarchs.
The Emperor arrived during a Great Hunt, the final one to be precise, and quickly swore his fealty to the Emperor, thus renaming the I Legion to The Dark Angels.
Lion El'Jonson won many victories across the galaxy in the time of the Great Crusade, but Luther and a handful of the Dark Angels were sent back to Caliban because of a mistake that could've killed them all. A nuclear bomb were smuggled up in a shuttle next to the Flagship of the Dark Angels during a treaty/bargaining for a group of people to join the Imperium.
Luther was then corrupted by Chaos due to jealousy and a little bit of hatred towards the Lion.
when Lion El'Jonson returned to Caliban, Luther ordered the orbital defenses to fire upon the Lion, thus a little war started. The Lion succeded in finding Luther and battle him, but was mortally wounded before a massive warpstorm hit Caliban and thus shattering all except the Order's Monastery, also called The Rock. Now, Luther is encaged within a stasis cell deep within The Rock, a secret known only to the Supreme Grand Masters of the Legion.
But no one knows that The Lion is still alive, safe for the Emperor. Lion El'Jonson is asleep within an inaccessible part of The Rock, awaiting for the time for when the Dark Angels needs their greatest victory
