Due to Covid that I’ve binge watched most of Cheers. In the grainy photo here I’ve put a yellow dot over a guy with a handlebar mustache. He’s in nearly every episode as an extra somewhere around the bar. He has sat on all sides at some point and many times can be found in the chairs by the entrance. He’s never said anything, but he interacted with Norm at one point taking car keys from him. He disappeared sometime during season four. He must be part of the crew as he gets ready to start laughing before jokes are told. Not sure why I’m curious but I am. Can anyone identify him?
Here is a good place to start your research:
Moved to Cafe Society (from GQ).
Wikipedia contradicts itself when you look at John Ratzenberger’s page. Instead of his character starting as a barfly it claims the following:
Ratzenberger played mail carrier Cliff Clavin on the sitcom Cheers . He had read for the part of Norm Peterson, but after the audition, he sensed that they were not going to give him the part. Sensing an opportunity, he asked if they had written a bar know-it-all, which the producers decided was a great idea
Also it claims that the actor has played a character in every Pixar feature film ever made.
Anyway sorry for the hijack. Please get back to your search for the random man.
Al Traina Jr.?
According to some lists, like this one, he’s one of the highest grossing actors of all time, if you use the methodology of adding the gross take of every movie they’ve had a role in, no matter how small. His total comes almost entirely from Pixar movies, with “The Empire Strikes Back” thrown in as well.
ThisIsTheEnd, who is Al Traina Jr.? There’s no one by that name listed in any of the obvious places. There was a famous Al Traina (who wasn’t a Junior), but he wasn’t an actor, and he would have been too old at that point to look like the character that you indicated in the picture. He didn’t have a son named Al Traina, incidentally.
You’re aware there was a LONG thread a few years back trying to identify a guest on Johnny Carson’s show who turned out to be Al Traina, right? 
In response to the OP, I’ve seen every episode of Cheers, and I don’t recall the guy in the photo ever having either a line or a character name.
I just had a scan through the crew, and none of the long-running stalwarts look like him, so I assume that means he was not a crew member who got to sit in as a background extra.
The closest lookalike I could find was the music composer, Craig Safan, but it’s not a very good match, and there’s no logical reason to have him on set. He likely composed a few pieces early on that then got reused a thousand times; he wasn’t hanging around next to the piano ready to go, or anything like that.
He was also the US Navy crew chief in Firefox, when Clint Eastwood landed on the icecap to refuel.
Wikipedia is correct though. I’ve seen interviews with John Ratzenberger stating the same thing.
Ratzenberger was also in the first Superman movie, starring Christopher Reeve, as a missile controller.
terentii, O.K., now I remember the long thread where we finally, after many guesses, identified the person in a picture as Al Traina. That was six years ago. I thought maybe the name Al Traina was familiar, but I couldn’t remember from where. Apparently there have been joking references in a bunch of threads since then to Traina, but those are threads that I didn’t read.
Right on! 
And he was NOT Peter Mark Richman! 
Yeah it was an Al Traina joke. I think it took 2 or 3 years to identify good old Al, or “Grimey,” as he liked to be called.
And Empire Strikes back, right?
Not Richard Masur, but sure could be his brother!
Side note: For years there was a facebook page that identified all the Roll Call extras in “Hill Street Blues.” They used mostly the same group thru the run of the show. Sadly that page has disappeared. Wish I had saved it.
Yeah, muldoonthief mentioned that upthread.
He got a bigger role in Superman II, as a NASA guy.
Clearly it is David Crosby.