Mike Wazowski (voiced by Billy Crystal) is a green monster with a ball-shaped body, a single big eyeball, two small horns, and skinny arms and legs.
In Monsters, Inc., Mike runs Sulley's station on the scare floor, and they are close friends and roommates. Mike has an outgoing personality and is dating Celia Mae. He has an ego that often makes him forget something obvious, such as his face being obscured in company advertisements.
Source: Wikipedia, "James P. Sullivan (Monsters Inc.)", available under the CC-BY-SA License.