Grimlock is an anicnet and powerful warrior who takes the form of a Tyrannosuaurs Rex from Earth. He is the leader of the mighty Dinobots.
While on Lockdown's ship, Grimlock was briefly seen when Lockdown was imprisoning and talking to Optimus Prime. It was later revealed by Lockdown that this place is the prison for the Legendary Knights, which were the Dinobots. Later, when the Autobots, Cade Yeager, and Shane Dyson arrived to rescue Optimus and Tessa, Hound flew this prison away(since it was a detachable part of the ship) and sent the Autobots to a trainyard while Crosshairs and Bumblebee were fighting against Lockdown's mercenaries. Later, when the ship arrived at Hong Kong and was ready to pick up KSI's CEO, Joshua Joyce, and the Seed, a Trax arrived and shot the ship, sending it pummeling towards the nearby Wulong Valley. Soon, Optimus freed the Dinobots and asked for their assistance to the Autobots. Grimlock, however, refuses and began attacking Optimus. Within minutes, Optimus beat the giant warrior, and Grimlock decided to join forces. Then, the Dinobots and the Autobots led a widespread rampage in which destroyed most of Galvatron's forces. After the rampage, Lockdown returned and attempted to retrieve Optimus, Grimlock, and the others with a giant magnet. However, Optimus saved the day by shooting towards the magnet. Later, his efforts were focused on blocking a bridge so that Galvatron cannot get the Seed. After the battle, Grimlock and his Dinobots left the Autobots with good terms, running off to the countryside during sunset.
In the years following the battle in China, Grimlock joined the Autobots in hiding at Cade Yeager's scrapyard. Unfortunately, he developed a habit of stealing the local sheriff's cruiser and using it as a chew toy. On the day Cade encountered a dying Cybertronian knight, he returned to find an angry sheriff demanding the return of his vehicle. Grimlock tried to hide the cruiser by eating it but was eventually berated into vomiting it back up. Cade then turned on his assistant Jimmy for not keeping Grimlock under control, who pointed out that without Cade the Autobots were uncontrollable and Grimlock had tried to eat him at least once. Grimlock later relaxed in the scrapyard while Cade called his daughter Tessa.
The next day, their refuge was discovered by the Decepticons and the T.R.F. forces. As their enemies prepared to invade, Cade and the Autobots escaped to a nearby town to carry out their emergency plan. Grimlock joined Slug in laying a trap for the pursuing TRF forces, bursting from beneath the road leading to the town and destroying the convoy. Grimlock then made his way to the town in time to save Cade and Izzy from Barricade, swatting the Decepticon with his tail, before slamming Megatron himself into the ground. As Dreadbot ran in to assist, Grimlock snapped him up and killed the Decepticon bank robber. He then turned his attention back to Megatron and Nitro Zeus, who quickly fled once Grimlock unleashed his considerable might upon the Decepticons. Grimlock remained in America after Cade was taken to England by Cogman and did not participate in the final battle on Cybertron.