Grimlock

Grimlock is a 15 year old male teenager, who was turned into a shapeshifter by Sera, but he betrayed after realizing that Sera was the villian and the Campers weren't. He and Kenji are at odds with each other, once even getting into a full on fight.

He shapeshifts into a Tyrannosaurus, but the doctor messed up and resulting in him being a little bit dimwitted. He doesn't even remember his name but Sammy gave him the name Grimlock after the Transformer.

Grimlock over the course of the third book attempted to fix his memory and voice, but failed after 3 tries. He is one of the 4 of the human campers left on Nublar (the others being Zach, Gray, and maisie)