The PM in Yes Minister.
Sitcom characters you never see Page 14
In The King Of Queens Arthur frequently tells his wartime stories from WWII and mentions a fellow soldier called "O'Shannon". At one point we learn that a shrapnel tore off O'Shannon's arm...and that he's dead.
Churchill in Then Churchill Said To Me....
Churchill in Dad's Army if you want to go that route. Hardly in keeping with the spirit of the original question though.
...and someone already posted "God in Father Ted" which kills every future joke in that direction.
Can't wade though all those posts........going to swear now as it is an American sitcom. 
Anyone mentioned Mrs Wolowitz in Big Bang?
Quote: Aaron @ December 18 2012, 1:40 PM GMTChurchill in Dad's Army if you want to go that route. Hardly in keeping with the spirit of the original question though.
No, he appeared in Shooting Pains.
Russell's boyfriend Bob in After Henry
I am going back over fifty years I know but Harry Worth used to refer to his Auntie on his Here's Harry sitcom, she was never seen onscreen. Here's Harry of course is famous for the iconic shop window scene on the opening credits.
Watching a Pointless today the question was to name KUA characters that have appeared in 20 or more episodes.
Someone said Sheridan and got the big red X !
Quote: Oldrocker @ March 2 2013, 12:27 AM GMTWatching a Pointless today the question was to name KUA characters that have appeared in 20 or more episodes.
Someone said Sheridan and got the big red X !
Ah, Pointless, the bastard lovechild of Family Fortunes...
Has anyone mentioned Monkey Harris in Only Fools and Horses, Del always seemed to be on the phone to him, but I don't remember him actually being on screen?
Richie Sister in Bottom. Aunt Rose in OFAH.
Paddy the Greek?
We never see Sheridan in Keeping Up Appearances.
Quote: G180e @ March 22 2013, 5:40 PM GMTWe never see Sheridan in Keeping Up Appearances.
That's mentioned three posts above.