The Yeti is a monster who worked at the Monsters, Inc. mailroom until he got exiled (presumably by Mr. Waternoose for tampering with mail) to the Himalayas. Despite being banished, he likes living in the human world.
He also made a cameo appearance in Monsters University as the Mailroom manager.
In Monsters, Inc., he is first mentioned by Mike Wazowski with Loch Ness and Bigfoot as the three monsters to all have one thing in common: banishment. Later, when Mike and Sulley get banished to the wasteland in the Himalayas, the Yeti greets them and makes them feel comfortable in his cave. He also shows himself to be a comedian, such as when he mentions about his friend Bigfoot, who has called himself "King Itchy." When he mentions something about a local village, Sulley, still wanting to help the human child he has accidentally brought into the Monster World, suddenly demands the Yeti to tell if there are any kids in that village so that he will be able to sneak back into the Monster World. However, the Yeti warns Sulley against going out in a blizzard, but Sulley does so anyway.
The Yeti is last seen calling to Sulley that he has made more snow cones (after the lemon ones had been used up as a tossing weapon by Mike), but Sulley either ignores him or is unable to hear him due to speeding down the hill on his makeshift sled.
The Yeti appeared at the end of the prequel as a Monsters, Inc. employee who introduces Mike and Sulley (then new arrivals) to their jobs as mail sorters. He tells them not to mess with the mail or peek into them, as such acts are punishable by banishment.
Monsters at Work
The yeti is expected to make a cameo in the series Monsters At Work.
The Yeti resembles Bumble the Abominable Snowman from Rudolph the Red-Nosed Reindeer.
The Yeti (called the Abominable Snowman), Bigfoot, and the Loch Ness Monster were all mentioned earlier by Mike to have been banished from Monstropolis when he was telling Sulley about what the consequences of their actions for helping Boo might be, possibly referencing the supposed existence of the real life versions of said monsters.
It is revealed in Monsters University that the Yeti was actually once a mail sorter at the Monsters, Inc. factory, but was banished to the Himalayas for accidentally messing up his job by tampering with the mail. This is also a homage to his voice actor's role as Cliff Clavin, the mailman in Cheers.
Despite previously working with Mike and Sulley, they do not seem to recognize each other in Monsters Inc.. Their entire conversation seems to suggest that the Yeti is just meeting Mike and Sulley for the first time.
In an M.I. book, Mike, Sulley, Boo and Celia take the Yeti back to Monstropolis.
The Yeti was parodied in the ending scenes of Cars, during the movie Monster Trucks, Inc., as the Abominable Snowplow.