Old One Eye is a unique Tyranid Carnifex with the ability to regenerate itself from mortal wounds. Its body bears the scars of many blows that should have killed it, and rumours persist among Imperial forces of Old One Eye being killed more than a dozen times. It is armed with a pair of huge, crab-like claws capable of ripping even the hardiest foe to pieces.
Old One Eye was the Carnifex who spear-headed the Tyranid Hive Fleet Behemoth's assault on the Ultramarines' world of Calth, swatting away Leman Russ Battle Tanks as if they were insects. Its rampage was stopped when a forgotten hero of the Imperium fired a Plasma Pistol through its eye and into its brain. This shot was the first time Old One Eye was brought down, and it is still unable to regenerate its eye and is permanently scarred with a plasma burn running across its skull.
Solar decades later, after Hive Fleet Behemoth had been driven from Calth, a band of smugglers stumbled across its body frozen intact in the ice-packs of Calth. They thawed it out, hoping to get a bounty for the corpse, but Old One Eye's grievous wounds instantly began to heal. It soon awoke and slaughtered the smugglers. Isolated from the Tyranid Hive Mind, a Carnifex reverts to its instinct to mindlessly kill, and so Old One Eye's release heralded a series of Tyranid raids on Calth. Land convoys were destroyed, hab-domes smashed and entire populations massacred.
Lesser Tyranid creatures such as Termagants and Genestealers, also left behind from Hive Fleet Behemoth's invasion, were drawn to Old One Eye's presence as a dominant Tyranid leader organism. The people of Calth cried out for aid, and they were answered by Scout Sergeant Telion of the Ultramarines.
Telion tracked down Old One Eye, but found it difficult to pierce its armoured flanks. As Telion's warriors were cut to pieces by the beast, Telion made a one-in-a-million shot that hit its ruined eye-socket. Old One Eye was overcome with pain and stumbled into a cavernous ravine. Telion led a search for the body, but Old One Eye was never found.
The eventual fate of Old One Eye is unknown, but there have been several reports of Carnifexes matching its description causing havoc across the Realm of Ultramar and beyond. If all the legends are true, then Old One Eye has been killed more than a dozen times.
Old One Eye's ability to heal damage inflicted on it during combat has given rise to theories of it being an unstable mutation, a Tyranid experiment in rapid cell regrowth abandoned by the Hive Mind. But with the arrival of the Hive Fleet Leviathan this mutation has become nearly a standard on every Carnifex.
The Genestealer Cult known as the Behemoid Undercult worships Old One Eye alongside its own Genestealer Patriarch. It is of such totemic importance to the Undercult that they ritually scar and tattoo themselves, or even cut out their own right eyes, in homage to the creature, seeing it as a prophet of the xenos god they simply call "Behemoth."
- Codex: Genestealer Cults (8th Edition), pg. 32
- Codex: Tyranids (8th Edition) pg. 61
- Codex: Tyranids (6th Edition) (Digital Edition), pp. 128-129, 161
- Codex: Tyranids (5th Edition), pg. 57
- Tyranids – The Carnifex Revealed (Defunct Link).