Randall 'Randy' Boggs (voiced by Steve Buscemi) is a purple, impatient, multi-legged lizard-shaped monster with a chameleon - like ability to change skin color and blend in completely with his surroundings.
In Monsters, Inc., he is Sulley's chief rival on the scarefloor; the two jockey for position as the area's top scream collector. He enters into a secret agreement with Henry J. Waternoose III, the company's CEO, to build a scream extraction device and use it on kidnapped children to solve the city's energy shortage. He eventually falls through a door into the human world and winds up in a house trailer whose inhabitants beat him senseless.
Source: Wikipedia, "List of Monsters, Inc. characters", available under the CC-BY-SA License.