From the Manufacturer

There was a time when the rage that boils inside Grimlock would have driven him straight to the ranks of the Decepticons. But while his flawed manner of speaking may make him sound strange, he's smart enough to recognize a bully when he sees one and Grimlock doesn't like bullies. It's this that fuels his dedication to the fight against the Decepticons. This dynamic dino will be your fiercest Autobot yet. Your Grimlock figure converts from dangerous robot mode to Tyrannosaurus Rex mode, with glowing eyes and mouth and a monster chomping jaw. Keep converting him back and forth so his Decepticon enemies can't keep up with him. Transformers and all related characters are trademarks of Hasbro.