Billy Crystal was the original first choice to voice Buzz Lightyear, but he turned the role down, which was a decision he still regrets. The next time that Toy Story creator John Lasseter offered him a role, Crystal accepted right away, becoming the voice of Mike Wazowski in Monsters, Inc.
As well as Billy Crystal, Jim Carrey was another top pick for the role, but Tim Allen was recast as Buzz once Disney gave Pixar a much smaller budget for the film than they anticipated.
Producers also originally wanted Paul Newman to voice Woody opposite Carrey (with Newman representing Old Hollywood and Carry representing New Hollywood) but again couldn't get Newman on board due to budgeting constraints.