Cyrius
From Lexicanum
Lord Commander Cyrius was an Emperor's Children's Space Marine Commander. He was the first to kill Lucius the Eternal, and was later damned to being trapped within his victim's armor for all eternity.
Heresy
Not much is known about Cyrius before the Horus Heresy, but it can be assumed that he turned traitor with his legion. He is known as the "Infamous Lord Commander Cyrius"1-p.57, and can therefore be assumed to be a well-accomplished soldier of Chaos as well as a commander.
Death
Cyrius took part in the legion's gladitoral games and killed Lucius, something thought impossible due to Lucius's inhuman skill and seeming unstoppable combat style. He did manage to defeat the depraved individual, but his victory was short-lived. The Prince of Pleasure, not willing to let such a promising protege die, turned Cyrius slowly and painfully into Lucius over a matter of weeks: "His hair fell out in clumps, and dark lines appeared under his flesh, slowly pushing through his skin as a maze of scar tissue. Soon Lucius had emerged completely, and all that remained of his executioner was a screaming, writhing face, subsumed for eternity into Lucius's armor".1-p.57
