Grem first appeared on the oil platform as one of the Lemons, who thought they killed Finn McMissile. He was next seen in Japan when he and Acer attacked Rod Torque Redline in the bathroom.
Rod then managed to pass along a device containing information to Mater (who happened to be there) regarding the conspiracy plot. Afterward, Grem tested the electromagnetic pulse camera that would be used to blow out the race cars during the World Grand Prix on Rod, killing him in the process.
Grem, accompanied by Acer, was assigned to use the camera on the race cars during the World Grand Prix. He aimed the camera beam at a racer and with the result of the Allinol heating up, blew out their engine. Grem and Acer also caused a big crash in Italy. After Mater, Finn, and Holley tried to stop the Lemons, they were all captured. Grem and Acer were then assigned to kill McQueen using the camera but since Sarge and Fillmore switched out the Allinol with Fillmore's organic biofuel mixture, the camera beam did not work properly.
When Mater discovered the bomb strapped to his radiator and McQueen chased Mater down to see what the situation was, Grem and Acer pursue them throughout London until Holley Shiftwell intervened and threw Grem and Acer off the road and into the Ye Left Turn Inn restaurant where they got beat up by an angry cars bigger and stronger than them. It is completely unknown what happened to Grem and Acer afterward, but it is likely that in case they were not beaten to death by the car clients (as they were just angry albeit most probably without murderous intentions), they were later taken into custody with the other Lemons.
Grem is shown to have several gaps in his teeth.
Grem's name is derived from Gremlin, albeit he's not related to the Gremlin family.