In 1959, Peter Sellers starred in The Mouse That Roared, a pretty good (I thought) little comedy film based on the novel of the same name by Leonard Wibberley. Mr. Sellers, as was his wont, played three roles.
Then in 1966, the novel was adapted as a potential TV series with Sid Caesar, who also often played multiple roles. In this case, he played the same three roles as Sellers. In support, Mr. Caesar had Joyce Jameson, Richard Deacon and several other faces (like that of Peter Leeds) that were quite familiar from TV shows of that period. Mr. Deacon, of course, was available because The Dick Van Dyke Show had just ended its glorious run.
A reader of this site who calls him- or herself "Orange Apple" sent me this link to the pilot. It was directed by Jack Arnold, who directed such great films as It Came from Outer Space, The Creature from the Black Lagoon, The Incredible Shrinking Man and the Peter Sellers version of The Mouse That Roared. The script was by Frank Tarloff, who spent much of his career writing for the top situation comedies (including The Dick Van Dyke Show) often under pseudonyms because of The Blacklist. Mr. Tarloff won an Academy Award for co-authoring the movie Father Goose and he also wrote one of my "guilty pleasure" faves, A Guide for the Married Man…in which Sid Caesar also appeared.
Of special note is the unusually-long theme song for which Allan Sherman not only wrote the lyrics but sang 'em. The pilot never became a series but you might want to give it a look. I can name worse shows from that period that did sell…some for more than one season.