Katsu

Katsu was a Sontaran who had a reputation for being the fiercest of all.

History
Katsu was a fierce warrior who was victorious in a thousand encounters and like all Sontarans sought battle. However it was on the planet Keth that Katsu lost a battle against a Levanaxus in which he had to escape in his ship and since then it haunts him everyday.

In a way to make sure he'd never lose again, Katsu sought to find the ultimate weapon to make him invincible. This brought him to the planet Aleph-777, a planet known for it's tranquillity where the inhabitants rely on the ultimate armament. Katsu started to kill the people on the planet till they'd give him the weapon. Eventually a man escaped with the weapon off the planet, Katsu followed the ship to where the man was taking the weapon.

Eventually Katsu tracked him to the planet Omega-666 where the man was supposably finding a place to hide the weapon. Katsu pushed the man aside and dug up the place but instead pulled out a metal flask. The man used reverse psychology telling Katsu not to open the flask but when did, Katsu was covered in the Omegan Green Plague which the flask contained which slowly dissolved away. (DWM: The Final Quest)