Pinky and the Brain

Context: Many of the Pinky and the Brain episodes occur in the 1990s at Acme Labs, located in some large American city underneath a suspension bridge. Several episodes take place in historical times, with Pinky and the Brain in the laboratory of some scientifically-minded person, including Merlin, H.G. Wells, and Ivan Pavlov. There is very little continuity between episodes outside of the common fixtures of the mice, though some plans for world domination from early episodes are subsequently referred to in later seasons (for example, Brain's "human suit" used in "Win Big" reappears when Brain faces his rival Snowball in "Snowball").  The bulk of every episode involves one of Brain's plans for world domination with Pinky's assistance and the ultimate failure of that plan, with some exceptions. One centers on Snowball's plan to take over the world using Microsponge (a parody of Microsoft). Another episode features Brain's single day where he tries to do anything but take over the world: in the end, a group of people vote that he should take over the world on the one day he does not want to.  Both Pinky and the Brain, white mice kept as part of Acme Labs' experimentation, have undergone significant genetic alteration; per the show's title lyrics, "their genes have been spliced" which gives the two mice amplified intelligence over that of a typical mouse, the ability to talk to humans, and anthropomorphism. "Project B.R.A.I.N." suggests that the gene splicing occurred on September 9, 1995, which is coincident to the first full episode of Pinky and the Brain. The episode "Brainwashed" states that the gene splicing was done by Dr. Mordough, along with Snowball the hamster and Precious the cat, using the Acme "Gene Splicer, Bagel Warmer, and Hot Dog Steamer."  Although Pinky and the Brain plan to conquer the world, they do not show much animosity. In a Christmas special Pinky even wrote to Santa that Brain had the world's best interests at heart.  Pinky (voiced by Rob Paulsen) is another genetically modified mouse who shares the same cage as Brain at Acme Labs. Although intelligent in his own right, Pinky is an extremely unstable and hyperactive mouse. He has several verbal tics, such as "narf", "zort", "poit", and "troz" (the last of which he started saying after noticing it was "zort in the mirror"). Pinky's appearance is the complete opposite of Brain's--while Brain is short, has a crooked tail and pink eyes, and speaks in a deeper, more eloquent manner, Pinky has a straight tail, blue eyes, and a severe overbite, is taller than the Brain, and speaks in a higher pitched voice with a Cockney accent. Pinky's name was inadvertently given to him by Brain himself: when insulting the two scientists responsible for their gene splicing while talking to himself, Brain claimed the scientists had "less knowledge in both their heads than I do in my... pinky!" Pinky then responded with "Yes?", believing Brain was referring to him.  Pinky is more open-minded, kinder, and happier than the Brain. Troubles never ruin his day, arguably because he is too scatter-brained to notice them. He steadfastly helps Brain toward world domination, even though Brain usually berates, belittles, and abuses him. Pinky actually seems to enjoy this, laughing after he is hit. He is obsessed with trivia, spending a lot of time watching television in the lab and following popular culture fads. Sometimes Pinky even finds non-rational solutions to problems. An entire episode (entitled "The Pinky P.O.V.") even shows a typical night of attempted world domination from his point of view, showing his thought process and how he comes to the strange, seemingly nonsensical responses to the Brain's famous question, "Are you pondering what I'm pondering?" Pinky often points out flaws in the Brain's plans, which the Brain consistently ignores. The issues Pinky brings up can ironically lead to the downfall of the given night's plot.  He is also arguably Brain's moral compass and only real friend. When Pinky sold his soul to get Brain the world in "A Pinky and the Brain Halloween", Brain saved him because he missed him and the world was not worth ruling without him. Pinky also has shown signs of intelligence despite his supposed childish stupidity. In "Welcome to the Jungle", Pinky was able to survive using his instincts and become a leader to Brain, who, despite his intelligence, could not survive in the wild on his own. And in "The Pink Candidate", when Pinky became President, he later began citing various constitutional amendments and legal problems that would bar Brain from his latest plot to take over the world. When Brain attempted to pressure him into helping, Pinky refused, claiming that the plan "goes against everything I've come to stand for."  Snowball the hamster (voiced by Roddy McDowall) is Brain's former friend who was also made intelligent by gene splicing and has a similar desire for world conquest (though far more malevolent than Brain's) which Pinky and the Brain are sometimes forced to stop.  Billie (voiced by Tress MacNeille) is a female mouse and another result of gene splicing. She is smarter than Brain and also has the goal of world domination. Though Brain loves her, she fancies Pinky. In the episode "You'll Never Eat Food Pellets In This Town Again", it is revealed that Brain is married to Billie (who in real life is Sheila, and hates playing Billie), who pretty much only agreed because he's famous, and eventually kicks him out and makes Brain live in his restaurant. It is later revealed that the events were just a dream.  Pharfignewton (voiced by Frank Welker) is a racing mare, with whom Pinky falls in love.  Larry (voiced by Billy West) is a white mouse who was created as a response to demands from Kids WB executives to include additional characters on the show. His presence is sporadic as the writers of the show believed that including an additional character would ruin the chemistry between Pinky and The Brain, as they worked best as a comedy duo, and a third character would therefore be out of place and unnecessary to the plot. To further drive this point home, Larry's first appearance was marked by a modified version of the theme song with the name "Larry!" shoehorned in between existing lyrics.  Other characters that have appeared on the show have included both of Brain's and Pinky's parents and the pair's "child", "Roman Numeral I" (Romy for short) who was a result of a cloning mistake. Episodes also include recurring caricatures of celebrities, including both Bill and Hillary Clinton, David Letterman, Dick Clark, Drew Carey, Ryan Stiles, Kathy Kinney, J. D. Wilkes, Paul Gilmartin, Annabelle Gurwitch, Don Rickles, Michael Keaton. Eric and Donny from Too Something, "Macho Man" Randy Savage, The Allman Brothers Band, David Cross, Jack Black, Chris Shiflett, and Christopher Walken, as was common on other Animaniacs cartoons. CANNOTANSWER

Question: who were some recurring characters on Pinky and the Brain?
Answer: Merlin, H.G. Wells, and Ivan Pavlov.