From Lexicanum

Decapitator is a Mandrake champion, and master assassain. Very little is known about him as he, like all Mandrakes, is incredibly elusive, living on the fringes of Commorragh. It is said that his lair is lined with thousands of skulls garnered from his many victims. None know his real name, but his weapon of choice and his killer's call sign have earned him the nickname Kheradruakh, or "He Who Hunts Heads".

Like other Mandrakes, he is entirely carnivorous, delights in the taste of living flesh, and has no qualms about eating other Eldar. Also like other mandrakes, he lives without any semblance of societal laws or restrictions. As such, the only currency he can be paid with is lives, many times earning literally thousands of slaves as payment to take a single head of his client's choosing.

Entirely unique to Decapitator, however, is the fact that he has had two additional fully-functioning arms grafted onto his body by the Haemonculi of Commorragh. This provides him with an uncanny strength and ability in melee combat which few are capable of matching.

Equipment

Decapitator

Decapitator's weapon of choice is a blade that bears his same title. It is said that no form of shield can protect from it. None who have seen it have lived to tell about it, therefore it is not actually known what type of blade it is, however it is believed to be a variation on the traditional Mandrake arm blade.

Sources

Codex: Dark Eldar (3rd Edition)

Dark Eldar Army List
HQ	Archite • Archon • Dracite • Dracon • Haemonculi • Incubus
Elites	Grotesque • Mandrake • Succubus • Warp Beast Pack • Wych
Troops	Raider • Sybarite • Warrior
Fast Attack	Hellion • Reaver Jetbike
Heavy Support	Ravager • Scourge • Talos
Special Characters	Asdrubael Vect • Decapitator • Drazhar • Kruellagh the Vile • Lelith Hesperax • Urien Rakarth