Brother Corbulo is Sanguinary High Priest to the Blood Angels. He holds the duties of a codex chapter's Master of the Apothecarion and shares certain duties with a Reclusiarch as he keeps many of the chapter's relics, though the Blood Angels do have their own chaplains. Of all the relics he keeps none are more treasured than the Red Grail that was used to catch the blood of Sanguinius after he was slain aboard the Vengeful Spirit and still it contains his blood after ten thousand years. Somehow. This chalice is used in the creation of all Blood Angels' recruits as drinking the blood of Sanguinius is the final step in the transformation into a marine (though this makes one wonder why the flying fuck Corbulo keeps carrying the thing into battle). Of all the Blood Angels Corbulo supposedly the truest of his father's sons, though not purely in the physical sense. He is said to have his father's deep wisdom and even his gift of foresight, a talent that has served his brothers well. Corbulo foresaw the second war for Armageddon long before it happened so the Blood Angels were some of the earliest to answer the world's call for help. Also notably an actual scientist in the traditional sense. Unlike the Mechanicum or the typical Apothecarium of your typical chapter, Corbulo and his subordinates actually use logic and experimentation to solve the gene-curse of the Blood Angels and their brother chapters, though this doesn't always work out the best for them.
On the Tabletop
In game Corbulo is a more expensive Sanguinary Priest with a few extra goodies. He has ATSKNF, and his foresight is represented by allowing you re-roll any dice roll made for Brother Corbulo, once per turn. His warlord trait is Gift of Foresight, giving him a 6+ FNP that can re-roll 1s, As far as gear goes he comes out of the tin with power armor, a Bolt pistol, frag and krak grenades, a narthecium, Heaven's Teeth (a unique chainsword with +1S -1AP 1D, but has no +1A) and The Red Grail, a relic blood chalice that adds +1 strength, and hit rolls of a 6+ grant another hit roll, which cannot generate more hit rolls for all blood angel units (but not successor chapters) within 6" of him, and that does count himself.
As far as actual tabletop worth, Corbulo is a very effective HQ choice, he's pretty cheap at 83 pts compared to the 60 pts of a sanguinary priest, alongside his upgraded chainsword, combined with the red thirst's +1 to wound in the fight phase when you charge, he'll wound anyone toughness 5 or less on 2s,toughness 6 on 3s and toughness 7 on 4s, which is impressive for a cheap infantry character, considering that he goes up to 5 attacks with Shock Assault, combine that with his warlord FNP and his reroll, and he can be both an effective support character for defensive strategies or a good assault character along with some DC units or some chainsword marines, though his 6" movement limits him if you pair him up with jump pack units.
Corbulo was a Roman General in the early Roman Empire. He committed suicide on the orders of Emperor Nero, screaming “Axios!” (I am worthy!) as he did it.