The Tsutsaroth, like the rest of the Avernic demons, were slaves of the ruling race of Infernus. Originally this was the Infernals, but the cannibalistic Chthonians managed to overthrow them and become rulers of the realm at a point thousands of years before the events of Palkeera's memory.
Avernic demons were used as shock troops in battle, led by Chthonian nobles. Zaros tricked the leader of the Chthonians into giving him command of twelve such legions of troops, and brought them to Gielinor. There, thanks to the efforts of Zaros' vast numbers of human followers, even the lowly Avernic demons lived in luxury among Zaros' elite.
The Avernic demons in Gielinor began to harbour rebellious thoughts against the Chthonians, who kept their distance from the "slave" troops that vastly outnumbered them. Zamorak played on this growing dissatisfaction, and used it to sway the Avernics into following him. There were, however, only two Tsutsaroth demons that were willing to pledge outright allegiance to the traitorous general.
On returning from his post-Ascension banishment, Zamorak kept his promise to the Avernics and led them on a twenty-year war in Infernus, that resulted in the death or flight of all the Chthonians. The remaining Avernic were fiercely loyal to Zamorak as a result, and were the backbone of his army in his battles in the God Wars.
The Tsutsaroth became feared by Zamorak's enemies. The desert city of Uzer was destroyed by Thammaron, although he was fatally wounded in that battle. Zamorak's general, K'ril Tsutsaroth, led an attempt by Zamorak's armies to steal the godsword from the other gods' forces, and he was frozen along with the other combatants in a cavern for thousands of years.