The Microwave Gremlin (also known as Grumpy or Spike) was one of the original Mogwai spawned from Gizmo in the first film, Gremlins, and was the only one of them besides Stripe that looked any different from Gizmo; he had a reddish brown fur color, was chubbier than the other mogwai, and was usually seen with his ears dropping down a bit extra. In the mogwai stage he seemed to be Stripe's right hand man in his schemes and was usually seen next to him. He assisted in tying up Barney (the Peltzer family's dog) and likely helped or at least planned in chewing through the wires in Billy's alarm clock so that he will feed them after midnight.
Grumpy had been spawned by the Mogwai known as Gizmo and had begun to live with Billy Peltzer, along with the other Mogwai created by Gizmo. Grumpy had been the right hand man to the leader of the evil Mogwai, Stripe, and had often assisted in carrying out his evil schemes. Like the other Mogwai (aside from Gizmo), had eaten the chicken Billy Peltzer gave them in order to become Gremlins. After eating it he hiccuped. The next day, he along with the others, entered his pupa stage inside their cocoons. Later that night they hatched and attacked Gizmo by tying him to a dart board and throwing darts at him. After Stripe disposed of Gizmo in the laundry chute, they explored the house. He and two of the others entered the kitchen and started to eat the gingerbread men Lynn Peltzer made. Lynn heard the noise and investigated the house. She grabbed a large butcher knife and snuck up on them. She killed one by turning on the blender while the gremlin had sat in it, and the other responded by throwing plates and other utensils. She defended herself with a tray and killed it by stabbing it with a knife. It is at this point in the film that we finally get a good look at Grumpy's gremlin form. He was physically larger than most of the other gremlins, but had their standard appearance. He did, however, have spiked eyebrows, bright red eyes, and little spikes on his head. He threw a tray full of gingerbread men he'd been eating at Lynn and growled at her for killing the others. Before he could attack Lynn, she sprayed him in the eyes with tick spray, blinding him. She then stuffed him in the microwave and turned it on. Grumpy struggled and moaned in pain for a while until his head exploded from the heat and pressure of the microwave, killing him instantly.
- The gremlin George from the sequel may be his incarnation because he reacts in anger to a microwave and destroys it by placing various utensils in it so it explodes and can't be used against him.
- The name of this creature is unknown, but fans has given him the nicknames Grumpy (due to his frequent scowling as a Mogwai) and Spike (because of the visible spikes on his head).
- This gremlin's death had been one of the causes for the MPAA to create the PG-13 rating for films, the other cause having been some of the gruesome scenes in the film Indiana Jones and the Temple of Doom. Gremlins had not received a PG-13 rating, but it's sequel had.