Some TMNT stuff really isn't for little kids.
Just as in the 1987 TV series, Tragg in the IDW comics is Krang's deputy commander and right hand. At one time, he and Granitor were subordinates of the tyrannical cyborgs 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 turning them into Rock Soldiers.
Tragg helped Krang in trying to conquer the home planet of the Neutrinos, and completely, escaped after the battle, in which the END rocket from Professor Honeycutt put all of the weapons of Krang's forces out of action.
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 Granitor, 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 Rock 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.