In order to fight the Teenage Mutant Ninja Turtles, Shredder concluded that he needed mutants of his own, and kidnapped a scientist forcing him to create mutants to serve him. Rahzar was mutated from a wolf cub, and believed Shredder to be his mother, at first Shredder believed the experiment to be a failure, and ordered Rahzar and the other mutant, Tokka to be destroyed, but then gave them a second chance after witnessing their brutally powerfull strength. The pair of mutants proved tough opponents for the TMNT, but during a battle in a night club, a chemical intended to reverse the TMNT's mutation was exposed to Tokka and Rahzar instead, restoring them to the animals they once were.
Teenage Mutant Ninja Turtles (2014 series)
Rahzar is a member of the Foot Clan much as he was in the movie/comic adaptation. However in the series he was once human, and intelligent.