The Collared Lizard, Crotaphytus collaris, (a.k.a. mountain boomer), is a North American lizard that can be up to a foot (30 cm) long, with a large head and powerful jaws. They are well known for the ability to run on their hind legs, looking like small dinosaurs. The collared lizard is the "state lizard" of the United States state of Oklahoma. The name "collared lizard" comes from the lizards' distinct coloration, which includes bands of black around the neck and shoulders that look like a collar.

These reptiles are often tamed and kept as pets. When born in captivity, they are quite docile and tolerant of interaction with humans. They are very active lizards, requiring a large amount of space to run. They prefer high temperatures, typically 105-110°F (40-43°C) at their basking spot and 80°F (26°C) elsewhere in their habitat during the day. Some collared lizards eat small amounts of fruit or vegetables, but most prefer a diet of insects. Like many reptiles, in captivity they must be provided a diet supplemented with extra calcium and a light source with ample UVB radiation to reduce the risk of bone disorders.

The origin of the name "mountain boomer" is unclear, but is thought to have originated among settlers travelling west during the Gold Rush. One theory is that settlers mistook the sound of wind in canyons for the call of an animal in an area where the collared lizard was abundant. In reality, collared lizards are silent.