Since he's TV's most memorable mailman, everyone knows John Ratzenberger's name. But his long-running stint as know-it-all Cliff Clavin on Cheers almost didn't happen.

"In the first season, I wasn't a regular," Ratzenberger, 56, recalls . "I invented the character in the audition, and from week to week, I didn't know whether I was going to do next week's show or not.

"[Once], after we shot an episode," he recalls, "they said, 'Your call time is 10 o'clock on Monday.' And I was looking at the script thinking, 'I'm not in this script.' I didn't want to embarrass anybody, so I walked up to [Cheers creator] James Burrows and said, 'I'm not in this script, so I won't be here on Monday.' And he said, 'What? We'll put you in.' The following year, I was made a regular. That was a big moment for me."

The comedy tried out many other bar flies, but none worked quite as well as Cliff. Ratzenberger thinks he knows why. "With a postman, you can bring in a lot of information from the outside world," he reasons. "Everyone else worked in the bar, including Norm — [sitting there was] all he did! It was like he had a job there."

Cheers isn't the only place this go-getter has made himself indispensable. He's lent his voice to all Pixar's animated features, including A Bug's Life, the Toy Story movies and Monster's, Inc. And he provides voices for an entire school of fish in their current hit, Finding Nemo! But will Ratzenberger, an avid fisherman, reconsider his hobby after doing this fish-friendly flick? "I'll make a promise," he winks. "If I find a fish that talks, I'll throw him back."