Actor Allan Melvin, who died recently, was a guest star on “The Andy Griffith Show” 8 times. He portrayed a different character in each episode. I know Rachel Dratch had a cameo as a different character on each episode of the first season of “30 Rock”, but other than that, who holds the record for portraying the largest number of different characters on a single television series?
I’ll go with Carrol Burnett, or one of the regulars on her show.
Regulars:
Vicki Lawrence
Harvey Korman
Tim Conway
Jeffrey Combs played many many roles in Star Trek (I think 7) . Not quite the same thing because he played them on several different series but all of them in the Star Trek universe. Most of the characters were important ones that had several appearances each.
I think the record has to go with Tito Fedderson, wife of producer Don Fedderson (parents of Mike Minor of “Petticoat Junction” fame). She had an uncredited “cameo” in just about every episode of “The Millionaire.” (Normally “cameo” refers to a brief appearance of a well-known actor/actress.)
But to add a few more names, Doug Mossman, Kwan Hi Lim, and Daniel Kamekona each played over 15 different roles in the 12-year run of “Hawaii Five-O.”
Surely the OP meant to exclude sketch comedy shows without a continuing narrative, or else Darrell Hammond of Saturday Night Live would win hands down.
Yes, I would exclude variety and sketch comedy shows. Situation comedies or dramas is what I was thinking of.
I first read this as “most different” meaning different in quality rather than quantity, and was going to suggest Garrett Dillahunt as the cockeyed gutter rat Jack McCall in season one of Deadwood, followed by the sophisticated, almost foppish Francis Wolcott in season two. Just two roles, but they were “most different”.
Just about every New Zealand actor on Xena and Hercules 
Honestly, I haven’t a clue. I completely would of missed all the said examples.
Dan Castellaneta, Harry Shearer, or Hank Azaria on The Simpsons?
I guess we’ll be excluding animated situation comedies now.
Not the record, apparently, but Wayne Alexander had five different roles on Babylon 5, one of them recurring.
Bonus points for Patty Duke for playing two characters at the same time for so long.
John Lovitz guest starred twice as different people on NewsRadio before becoming a regular as a third character.
Clark Howat, Art Balinger, Al Shelly, Virginia Gregg, and Ed Deemer all played 10+ different roles in the four year run of the 1960s “Dragnet.” Jack Webb had a pool of actors that he recycled a lot.
Maybe not hands down; surely he has some rivals. For instance, Bob Odenkirk and David Cross sometimes played multiple characters within the same sketch on Mr. Show.
That’s what I would have said. Virginia Gregg was the first one who popped into my head.
Scott Bakula played at least two characters (himself and the person he leaped into) in every episode of Quantum Leap. There were 95 episodes so that puts his total at at least 96.
Larry David played many characters on Seinfeld. He was the first Newman, Steinbrenner, Mr. Costanza’s accountant, a jerk on a plane, a mad scientist (or spaceman or something) in a TV show Jerry was watching, and a few other characters. Don’t have a complete list.
In the old detective series Columbo, they re-used actors many times in different roles. A guy named Michael Lally was in at least 19 different episodes, each time as a different character.
Granted that many of those weren’t much more than an extra in the background, still he was there.
Also in Columbo, John Finnegan was in 11 episodes as about 9 different characters (he repeated the character of Barney the Café Owner in about three episodes).
And Peter Falk’s wife, Shera Danese, was in 6 episodes, all fairly big parts, all different characters.
But Mike Lally at 19 seems to be up there for the record.
Assuming animated series have not yet been eliminated, Lovitz also “appeared” on the Simpsons’ at least five times in separate roles and, I believe, three times as Artie Ziff.
Terry O’Quinn played 3 different characters on The X-Files, two in the TV series and one in the movie.
Mel Blanc played quite a few characters on the Jack Benny Program over the years.