Doug's Doug Funnie and The Ren & Stimpy Show's Ren and Stimpy
Voiced by: Billy West (although he only voiced Doug during the show's run on Nickelodeon from 1991–94).
Fun fact: West is also best known for being the voice of Fry on Futurama.
Disney's House of Mouse's Minnie Mouse and The Simpsons' Martin Prince
Voiced by: Russi Taylor.
Fun facts: Taylor has voiced Minnie Mouse since 1988 (she is only the fourth person to do so). She has also provided the voice of such memorable characters like Gonzo on Muppet Babies, and Webby Vanderquack, Huey Duck, Dewey Duck, and Louie Duck on DuckTales, as well providing the voices of Üter, Sherri, and Terri on The Simpsons.
Tiny Toon Adventures' Buster Bunny and Aaahh!!! Real Monsters' Ickis
Voiced by: Charlie Adler (although he only voiced Buster Bunny for the show's first two seasons).
Fun facts: Adler, who began his voice-over career in 1984, has also voiced characters on '80s classics Jem and G.I. Joe, as Eric Raymond and Low-Light, respectively, as well as providing additional voices for characters on '90s cartoons such as Captain Planet and the Planeteers, Rocko's Modern Life, Eek! the Cat, and Darkwing Duck.
The Simpsons' Bart Simpson and Kim Possible's Rufus
Voiced by: Nancy Cartwright.
Fun fact: Cartwright also voiced spoiled-brat Pistol Pete on Goof Troop.
Muppet Babies' Animal and Bobby's World's Bobby
Voiced by: Howie Mandel.
Fun fact: Aside from Animal, Mandel also voiced Skeeter and Bunsen on Muppet Babies from 1984–85.
Goof Troop's Pete and Darkwing Duck's Drake Mallard/ Darkwing Duck
Voiced by: Jim Cummings.
Fun fact: Cummings also voiced characters on five other Disney Afternoon shows: DuckTales, Chip 'n Dale Rescue Rangers, Quack Pack, TaleSpin, and Bonkers.
Futurama's Bender and Kim Possible's Dr. Drakken
Voiced by: John DiMaggio.
Fun fact: DiMaggio is probably best known today as the voice of Jake the dog on Adventure Time.
Chip 'n Dale Rescue Rangers' Gadget Hackwrench and The Simpsons' Agnes Skinner
Voiced by: Tress MacNeille.
Fun facts: Along with Agnes, MacNeille also does the voices of Simpsons recurring characters Cookie Kwan, Brandine Spuckler, Dolph, Lindsey Naegle, Bernice Hibbert, and the Crazy Cat Lady.
Other characters MacNeille has voiced include Dot Warner on Animaniacs, Babs Bunny on Tiny Toons, and Charlotte Pickles on Rugrats.
SpongeBob SquarePants' Mr. Krabs and Superman: The Animated Series' Lex Luther
Voiced by: Clancy Brown.
Fun fact: Brown has lent his voice to various comic book–based animated series, including Justice League, The Spectacular Spider-Man, The Batman, and Wolverine and the X-Men.
The Smurfs' Papa Smurf and Scooby-Doo, Where Are You!'s Scooby-Doo
Voiced by: Don Messick.
Fun facts: Aside from originating the voice of Papa Smurf and Scooby-Doo, Messick also provided the voice of Bamm-Bamm Rubble on The Flintstones, Boo-Boo Bear on The Yogi Bear Show, and Hamilton J. Pig on Tiny Toons.
Rugrats' Tommy Pickles and The Powerpuff Girls' Buttercup
Voiced by: E.G. Daily.
Fun fact: Daily took over the role of Babe in Babe: Pig in the City, from her Rugrats' co-star, the late Christine Cavanaugh (who voiced Chuckie), who was the voice of Babe in the first film.
The Real Ghostbusters' Egon Spengler and Animaniacs' the Brain
Voiced by: Maurice LaMarche.
Fun fact: LaMarche went on to voice Kif Kroker on Futurama.
Animaniacs' Pinky and Teenage Mutant Ninja Turtles' Raphael
Voiced by: Rob Paulsen.
Fun fact: Paulson also voiced Yakko Warner and Dr. Otto Scratchansniff on Animaniacs.
Darkwing Duck's Megavolt / Elmo Sputterspark and The Simpsons' Homer Simpson
Voiced by: Dan Castellaneta.
Fun facts: Castellaneta might be synonymously known as the voice of Homer Simpson, but, in reality, he has actually had a rather extensive voice-over career. He has voiced characters such as Arnold's Grandpa Phil on Hey Arnold!, Earthworm Jim on Earthworm Jim, and the Genie in Aladdin (the TV series).
Scooby-Doo, Where Are You!'s Fred Jones and Transformers' Megatron
Voiced by: Frank Welker.
Fun fact: Welker was the original voice for the character of Fred and, since 1969, has continued to play him in almost every animated adaptation and reboot of the series.
The Flintstones' Barney Rubble and Heathcliff & the Catillac Cats' Heathcliff
Voiced by: Mel Blanc.
Fun fact: Known as "The Man of 1,000 Voices," Blanc was literally the voice of almost every single classic cartoon character, including Daffy Duck, Woody Woodpecker, Porky Pig, Tweety Bird, Sylvester the Cat, Yosemite Sam, and of course, Bugs Bunny, whom he continued to voice up until his death in 1989.