Grumpy is a Tyrannosaurus Rex who appears as one of the main villains in the 1974 TV series Land of the Lost and later as the (former) secondary antagonist in the 2009 movie of the same name.
Land of the Lost (1974 TV Series)
Grumpy appears frequently in the TV series. He is always shown chasing the Marshalls and trying to eat them. He is feared by everyone in the Land of the Lost, except by the Allosaurus Big Alice and the two fought each other on occasions, though in one episode they team up to try and hunt down the Marshalls. He was the first dinosaur the Marshalls encountered and the one who caused Cha-ka to fall and fracture his leg in the first episode.
Land of the Lost (1991 TV Series)
Some fans speculate that the T-Rex Scarface from the 1991 series is actually Grumpy of the original series.
Land of the Lost (2009 Movie)
Three years before the film events, an astronaut was transported in the Land of the Lost after passing in a time warp. Grumpy finds him and devours him.
One day, the paleontologist Rick Marshall and his friends Holly and Will arrive in The Land of the Lost. Shortly after their arrival, they fall into Grumpy's pantry (where the astronaut's spacesuit is also present) and they are grasped by living plants. Grumpy then comes and tries to eat them, but they manage to freed themselves from the plants and run away, pursued by Grumpy. Finally, the trio crosses a bridge too thin for Grumpy, which abandons the pursuit. However, he hears Rick claiming that the Tyrannosaurus is unable to crosses the bridges because he is not enough athletic and his brain has the size of a nut, which makes him very furious and convinces him to jump over the bridge. He pursues the group again (especially Rick), but they find refuge in a cave.
At night, Rick claims one more time to Will that the Tyrannosaurus has a brain of the size of a nut, but Grumpy comes at the entrance of the cave and deposes an enormous nut, then he throws a dark look to Rick.
During the following day, the group hears Grumpy's roar in the jungle. Later, they stumble upon a desert where many things from across time end up. After they saw a pack of dromaeosaurus attacking an ice cream truck, Grumpy appears and scares away the other dinosaurs. However, a female Allosaurus named Big Alice arrives and she and Grumpy start to battle out until they sense Marshall and choose to chase him. Rick tries to run by zigzagging to confuse Grumpy, but it proves ineffective and the T-Rex devours his backpack. Rick is then attacked by Big Alice, but Grumpy, who wishes to kill him himself, interposes and confronts the Allosaurus. Big Alice apparently escapes him or possibly defeats him because soon after she attacks Rick again (and is killed), while Grumpy doesn't reappear during this scene.
Much later, the trio is confronted to Enik, who sends Grumpy to attack them. He lets Holly and Will leave and confronts Rick. The latter tries to fight with a baton, but he is finally devoured alive, which horrifies Holly. However, Grumpy defecates Rick afterwards and the two manage to befriend. Rick uses Grumpy to attack all the Sleestaks controlled by Enik and the T-Rex succeeds in defeating the entire army by himself. Then, Rick says goodbye to his new friend, who pushes a huge roar.
Unlike the majority of hungry predators in fiction as well as his previous incarnations, Grumpy has a mostly complex personality. Though at first his only goal was simply to eat the protagonists, he later developed a vendetta against Rick for insulting him (he got angry for having Rick believed him to be stupid just because his brain is around the size of walnut). He also attempted to prove his intelligence (notably by sending a giant nut to Rick), which shows his susceptibility. He didn't want to kill Rick for sustanance, but for revenge, to the point that he even confronted Big Alice to be able to kill him himself. On the other hand, he didn't particularly hate Holly and Will and let them leave during his final confrontation with Rick.
However, after eating and defecating Rick where the latter proved that he survived over the course of his trip in his digestive system when devoured alive, he became much more friendly and turned friend with Rick and the others.