Welker’s Wikipedia entry doesn’t highlight “main” versus “recurring” roles, but he’s done voices for literally hundreds of animated TV series dating back to the late '60s, and typically provided the voices for both main characters (like Fred in the various Scooby-Doo series, as noted), as well as for several minor characters and “additional voices” in any given series.
Frank Welker credits, on series where he was, as far as I can tell, doing a voice for a main character in every episode (or close to it). This only goes through the late '80s; he’s still working today.
Also: gads, there was a crap-ton of cheap, bad kids’ cartoons in the '70s and '80s!
Scooby-Doo, Where Are You?
The New Scooby-Doo Movies
Super Friends
Wheelie and the Chopper Bunch
Jabberjaw
Dynomutt, Dog Wonder
The Scooby-Doo/Dynomutt Hour
Laff-a-Lympics
The Robonic Stooges
Dinky Dog
Fangface
Yogi’s Space Race
The New Fantastic Four
The New Adventures of Mighty Mouse and Heckle & Jeckle
Thank You @kenobi_65, Welker is probably the English speaker to beat.
@Czarcasm, should probably have categories.
Live Action
Lead
All types of regulars.
Someone could go digging and find a certain venerable Japanese voice actor who probably has Welker beat by a lot, but I’m not into anime, especially older anime enough to find him.
The top 10 might all be Anime voice actors, that seems likely.
Tom Kenny for example, has 330 SpongeBob episodes under his belt. That’s a whole lot of episodes.
That said, Google Gemini says that Ted Danson is the live-action champ with 12 series, and Frank Welker is the animation champ and the most prolific TV actor in history, with 800 credits to his name, and dozens of shows where he was a regular- just the set of Scooby Doo series is more than 12.
What was more interesting were the runners up. Dee Bradley Baker is the next most prolific voice actor, and John Larroquette is the live action runner up with 8 series.
And in a weird parallel runner-up category is David Boreanaz, who’s the winner for most consecutive years as a series regular, with 25 spread across four series.
The main six voice actors on The Simpsons – Dan Castellaneta, Julie Kavner, Yeardley Smith, Nancy Cartwright, Harry Shearer, and Hank Azaria – are all at around 800 episodes, as the show is now in its 37th season, and all of them have been with it from the start.
Elizabeth Mitchell ranks up there somewhere (Juliet from Lost). Around 2011-2012, I thought she was gonna show up on pretty much every show.
She was main cast on
Loving
LA Firefighters
Significant Others
The Beast
The Lyon’s Den
Lost
V
Revolution
Crossing Lines
Dead of Summer
First Kill
The Santa Clauses
So 12. Plus 7 television films and an unseemly number of unsold TV pilots.
She has been in a lot of shows, for sure, and always in the top billing slot. I don’t think this should directly impact her status here but the majority of those shows didn’t last a full season, or her role was only a single season.
Her most episodes were Lost (57), Loving (49) Revolution (42), V (22) and The Lyon’s Den (13). All the rest are between 6 and 12 episodes, one is listed in IMDB as a mini-series but I don’t think it really was. It was just cancelled after 3 episodes. She had guest roles that had more episodes than most of her starring roles, such as ER (14) and Once Upon a Time (10)
He’s not going to outdo some of the ones already mentioned, but Bill Bixby deserves a mention. He was a regular on My Favorite Martian, Hollywood Squares, The Courtship of Eddie’s Father, The Magician, Once Upon a Classic, The Incredible Hulk, Goodnight, Beantown, and True Confessions. That’s a pretty good record for an actor back when there were only three television networks.
Tom Kenny just popped into my head as having done a lot of shows, but I hadn’t thought about Dan Castellanetta or anyone else from The Simpsons
Regardless, there’s something to be said for having done 37 seasons of a show, versus 12 shows. I’m not sure one is more impressive than the other, honestly.