Some TMNT stuff really isn't for little kids.
At one time, he and Tragg were subordinates of the tyrannical cyborg Traxus. But after Traxus was killed by Krang in single combat, they voluntarily submitted to him. They were later (probably the very first of Krang's followers) to be given their characteristic stone skin by a preparation in Baxter Stockman's workshop making them Stone Soldiers.
Granitor commanded an assault on a Neutrino resistance bunker, to capture the Professor Zayton Honeycutt (the "Fugitoid") and bring him back to Krang. Due to his command the Neutrino bunker was destroyed and many innocent Neutrinos killed along with the Fugitoid's family. Later on he and several other Stone Soldiers was searching the demolished base for the Fugitoid. Granitor realized that the Fugitoid was in fact Honeycutt and chased him trough a portal to Earth. However, the Fugitoid used his morphing abilities to shapeshift himself into a human-looking disguise as Chet Allen and disappeared into the crowd.
He was later involved in the battle between Krang's forces and the Foot Clan on Burnow Island, and was one of the few there who was not killed by the terraforming that took place. Along with Tragg, he survived for several weeks in a cave that temporarily contained breathable air, but were slowly dying as the atmosphere changed. When Leonardo and Raphael came to investigate the murder of an Utrom, the two Stone Soldiers held the Turtles at gunpoint and demanded their oxygen breathers. In their weakened state, they were defeated easily by the Turtles, and were then attacked by the mutant Leatherhead.
Granitor was imprisoned by the Utroms for some time after that, but was freed by Ch'rell and became his loyal follower.