It must be accepted that everybody in Earth Prime has a counterpart in Earth Prime-Time. With the proliferation of home videos shown on series like 'America's Funniest Home Videos' and uploaded to Facebook and YouTube, eventually you probably will be a citizen of Toobworld.
And that has to be especially true for actors even if they already exist in that TV Landscape as other characters. Many of the more celebrated actors might show up in sitcoms and even dramas as members of the League of Themselves. Peter Falk played Daniel J. O'Brien and Lt. Columbo but he also appeared as himself in an episode of 'The Larry Sanders Show'. It's a hazard that must be accepted by televisiologists.
Check out this short clip from 'Get Smart':
So Martin Landau was one of the many famous actors who did quick cameos on that spy sitcom but he wasn't playing himself; in fact, he was Maxwell Smart.
However, the Chief mentioned Martin Landau by name which verifies his existence in Toobworld even if he wasn't technically "seen".
The best part is that this wasn't a Zonk! There was no mention of 'Mission: Impossible'. Alls we know is that Mr. Landau was playing a spy on television at the time. Actually it might not have even been a TV role; his fictional televersion could have been starring a spy movie franchise.
I'm beginning to think I could run with "Landau Gentry" blog posts until I get tired of it. Not really concerned how you feel about it. LOL
Would that be something that you would be interested in?