Zahariel

Zahariel was a bad-ass Librarian of the First Legion during the Great Crusade and later joined Luther in exile on Caliban due to inexplicable orders of their Primarch Lion El'Jonson, despite being one of the most idealistic Space Marines you'll ever find.

Also; if you believe half the forums on the internet a potential candidate for the secret identity of the Fallen Angel Cypher (more on that below)

No model or rules yet exist for him in Forgeworlds Horus Heresy series, and may never exist, but we can only hope.

Back Story

Before the Imperium turned up, as a child of about seven years old he and his cousin Nemiel joined the The Order (a knightly order where Lion El'Jonson was grand master) after spending a night stood to attention without moving, outside of their fortress walls... without shoes or a coat... ON A DEATH WORLD.

After a few year and a cliche training montage, he loses his mentor and hero to a Beast of the Forest, so naturally he goes on an EPIC QUEST FOR VENGEANCE!

On the road discovers Watchers in the Dark who of course tell him "BEWARE", "THE FORESTS ARE HAUNTED", "TURN BACK", "YOU HAVE A SECRET HIDDEN POWER" and all that cliched shit, he continues on his merry way and eventually slays the beast.

Oh... the beast happens to be a Calibanite Lion; the biggest, nastiest beast on the planet, and only the Lion has ever killed a Lion before. Zahariel could only accomplish this by using his INNER POWER where he managed to slow down time enough that he wouldn't get chomped to bits and was able to phase through the thing to hit its weak point.

Suffice to say this makes him a bit special, so he returns home the cliche hero and gets a sword made out of one of the Lion's teeth, and the Lion makes a few pointed remarks about him being the only other one to have a lion sword just like it.

Then they do a bit more war and eventually take over the planet Just as Planned. Also wiping out the conservative Knights of Lupus on the way, who wanted to keep the beasts around to keep their knightly way of life relevant (but apparently worshipped Chaos after all).

Then the Emperor turns up, shit breaks loose and he becomes embroiled in a taliban plot to bomb the parade. Zahariel is innocent though and uncovers the plot before it happens, gaining himself a personal audience with the Emperor, which he subsequently forgets due to mind wipe bullshit.

Then he and his cousin get drafted into the Dark Angels of course, Zahariel being one of the very first new Calibanite space marines... perhaps the first actually guaranteed to be admitted entry due to his psychic powers.

Zahariel becomes a Librarian while Nemiel becomes a Chaplain and all was well.

...Then he got sent home with Luther and a bunch of other brothers, becoming more important, eventually sortof becoming Luther's second in command.

He meets the Watchers in the Dark again who tell him how fucked up Caliban went, since they killed all the beasts in the forest that were guarding (and soaking up the energies of) the tainted locations cause the planet had been hiding a dark secret since the beginning of time apparently (it is really close to the Eye of Terror), and now that shit was waking up.

Luther (who in the mean time had been reading books from the Knights of Lupus) discovers some terrans doing a ritual apparently to summon a daemon. He and Zahariel go to break that shit up. Zahariel dies.

BUT Luther brings him back from the dead using "Advanced Medicine" and all is well.

...Until the Fall

Cypher?

Zahariel is a strong contender for the secret identity of Cypher, though that's nowhere near resolved yet, either in the 30k fluff or 40k fluff.

Lots of circumstantial evidence points towards Zahariel becoming Cypher after the heresy,

• The prologue for Descent of Angels is Cypher self-referencing, then in the story-proper Zahariel is pretty much the protagonist for both Dark Angel Horus Heresy novels (and one audio book where the then-current Cypher shits a brick and flees from Caliban's ancient terror)
• He's always made out to be the good guy
• He's one of three people in the Horus Heresy confirmed to have contact with the Watchers in the Dark (the others being Lion El'Jonson & Garviel Loken)
• While Cypher's tabletop rules do not have Psyker, Zahariel's power-set accounts for Cyphers buffs, such as the ability to slow time Matrix-style (hence Cyphers bullshit ballistic skill and Initiati)