Some Autobots wonder why Grimlock is even on their side. His disposition is much more suited to the Decepticons. After all, he values power and strength over wisdom and compassion, and furthermore, he doesn't really get along with most Autobots. When faced with a problem, his usual responses are to slice it with his energo-sword, tear it to pieces with his bare hands, or outright eat it. He is more willing to accept casualties than most of the Autobot leadership, and doesn't seem particularly concerned about the fleshies either. These things, coupled with his like of Optimus Prime, have led to a defection or two on Grimlock's part. He'd have no problem offing the Autobot leader if he thought he could get away with it, though.
What the Autobots don't realize is that the only thing he hates more than weakness is those who abuse their strength, meaning when push comes to shove, Grimlock will always fall in on the right side of the fence. And despite their disagreements, Grimlock holds a respect for Prime's strength and leadership.
Grimlock is the leader of the Dinobots, a small but powerful strike squad. Grimlock himself is extremely strong and durable, and is one of the few Transformers who can not only stand toe-to-toe with Optimus Prime and Decepticon, but actually give them a run for their money. Despite his strength and prowess, Grimlock continually struggles with his pronouns.
His alt-mode is a robotic Tyrannosaurus Rex.