Grimlock is a wild card among the Autobots. Huge and powerful, he is also ego-maniacal, impatient and willful. He views Optimus Prime as a weak leader, too afraid to make the tough calls and act on instinct. As such Grimlock is more than ready to disobey orders if he thinks the ends will justify the means. His one obvious redeeming feature is his attachment to his team. As leader of a Wrecker team called: the Lightning Strike Coalition Force, he has gathered together a group of similar minded individuals he would do anything for. Together they handle the jobs the Autobots don't have the stomach for.
Shockwave's experiments not only granted Grimlock a new alternate form, but increased his power tenfold. Unfortunately this was at the cost of his intelligence. While he is far from stupid, Shockwave's experiments have made it more difficult for the former field commander to think rationally and made his already prominent rage issues all the more severe. Fortunately his team, reborn as the Dinobots, have become more tight-knit than ever. Together they are helping overcome his disgust at what Shockwave has done to him and see the advantages of his new power.
Grimlock was a gladiator from Kaon, but chose to join the Autobots early on in the war. His has neutral views of Optimus Prime and shock and awe approach to combat meant he was not regarded as a great leader, but he has survived long enough to earn a high rank of the Wreckers and command of the Lightning Strike Coalition Force.
Grimlock is known for not following orders or trusting in Optimus Prime's ability to be an effective leader. As the leader of the Lightning Strike Coalition Force, Grimlock enjoys smashing things first and asking questions later. Due to Shockwave's experiments, Grimlock has been left with a malfunctioning voice processor and an alt-mode inspired by a distant primitive world.
Once he had a veichle mode of a Cybertronian tank, but after being experimented by Shockwave, Grimlock was reformatted with a beast mode of Cybertronian Tyrannosaurus Rex (T-Rex).