He was voiced by David Lander, who also played Smarty in Who Framed Roger Rabbit.
Thumper first appeared at the beginning of the film with the other grasshoppers, held on a leash. In order to maintain control over the ants, Hopper captures Dot and brings her really close to Thumper, who was snarling and growling. Then Flik yells at Hopper to let her go. Hopper's response is to double the food order before flying off with the other grasshoppers.
Thumper was later seen at the grasshoppers' home, laughing with the other grasshoppers when Hopper expressed concern about Flik standing up to him. Then he killed three grasshoppers and told the others that the ants outnumbered them 100 to 1 and that they are going back to keep them in line. Thumper and the grasshoppers then flew to the ant hill.
When Hopper was dissatisfied with the food, he orders that every scrap of food on the island be given to him and Thumper is shown growling at the ants. When Dot goes to find Flik, Thumper finds her and chases her until she falls off a rock (which, to the ants, is a cliff) to her supposed death. Thumper then flies away, only for Dot to emerge, flying for the first time.
Thumper is shown growling at Manny when he tries to do a circus act on the Queen, but Hopper told him not to. Then a model bird the ants made is unleashed, scaring the grasshoppers, only for P. T. Flea to set it on fire who accidentally aids Hopper. When it is revealed it was Flik's idea to build the bird, Hopper orders Thumper to beat him up. When the ants revolt, Thumper tries to scare Dot one last time, only to be slapped in the face by her and being called a "bad grasshopper" and told to go home. Enraged, Thumper roars at Dot, only for Dim to land behind her and roar at him like a Tyrannosaurus rex. Scared out of his wits, Thumper immediately flies off with the other grasshoppers, whimpering like a dog.
Thumper is very temperamental and mentally ill. He is known for being primal and animalistic in terms of both mannerisms and intellect.
Interestingly, in the movie's bloopers where the characters of the film portrayed as actors whom forgetting their lines, making a mistake or just being silly during filmmaking sequence, Thumper is revealed to be intelligent and persuasive, so he can speak instead of being the grasshopper gang's war dogs.
As he was roaring at Dot, he stops to rethink on how he could do better and apologizes for messing up before saying, "Can we cut? It's just that I don't think I'm coming across. Hmm. Oh! Oh! I know! I know! I could lather up a bunch of spit. Ooh, ooh, that's good. I got it, J.L. Alright, one more for me.
Thumper is depicted as a slender grasshopper whom in his debut, wearing a leash and collar like a dog and the shape of his head vaguely resembled human skull compared with the rest of other grasshoppers.
- Thumper's ironic name was completely intended: Director John Lasseter named him after his one of his favorite Disney characters from Disney's Bambi and just loved tasting the irony of it.
- During the outtakes, Thumper was voiced by David Lander, who also voiced Smarty the Weasel in Who Framed Roger Rabbit.