who does mike's voice in monsters inc
Billy Crystal.
Monsters, Inc.
 Billy Crystal, having regretted turning down the part of Buzz Lightyear years prior, accepted that of Mike Wazowski, Sulley's one-eyed best friend and scare assistant. 
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Monsters, Inc. [SEP] Casting
The casting of Steve Buscemi as Randall, Sulley's rival, saw a reunion between himself and John Goodman; they had previously worked together on "The Big Lebowski" and "Barton Fink".