Kleitus was the Captain of the elite 1st Company of the Imperial Fists Chapter of Space Marines. He died during the Imperial Fists' siege of Haddrake Tor when the Forces of Chaos proved capable of manipulating the Warp using sorcerous rituals in such a fashion that Kleitus and much of the 1st Company suffered from a teleportation mishap.
Kleitus rematerialised with one side of his body within solid rock, leading to an agonising death. Before he expired, he handed his great Thunder Hammer, the Fist of Dorn, on to Captain Darnath Lysander of the 2nd Company. Lysander went on to lead the Imperial Fists to victory over the Heretics and to be raised to replace Kleitus as the Captain of the 1st Company. Lysander still proudly wields the Fist of Dorn.
- Codex: Space Marines (5th Edition), pg. 91
- Codex: Space Marines (4th Edition), pg. 47