This is a minor point but it oughta be corrected somewhere on the web and I guess it's up to me…
Most of the press service obits for Kenneth Mars say something like "…he did a significant amount of voiceover work for animation, starting with TV's The Jetsons in the early 1960s." Yes, he did a lot of voice work in cartoons but no, not on the early 1960s Jetsons show.
There were two batches of Jetsons cartoons made for TV — one for the ABC network that aired from 1962 to 1963, then a syndicated version that first aired from 1985 to 1987. The original featured the voices of George O'Hanlon, Penny Singleton, Daws Butler, Janet Waldo, Jean Vander Pyl, Mel Blanc, Don Messick, Howie Morris and only one or two other folks, none of whom was Ken Mars. The first five or six of these actors were in every episode. The last two or three were in many but not all.
The syndicated revival featured all those folks plus many others in guest roles. One of these many others was Ken Mars. When these new shows aired, the old ones were intermingled and a lot of folks got very confused as to what was from 1962-1963 and what was from 1985-1987. The Internet Movie Database tries to treat it all as one program that started in 1962 and ended in 1987 so I have friends who did the show the first time in 1986 and suddenly they have a credit from '62. Writers, animators and production personnel are similarly and misleadingly identified.
To the best of my knowledge, Kenny Mars didn't start doing cartoon voices until around 1975, probably starting with his work for the animated segments on Uncle Croc's Block for Filmation. If I'm wrong, it's not by more than a year or so.