Unnamed TV scientist is a scientist who appears sometimes in the show.
He first appeared in a fictional sci-fi movie that Phineas and Ferb were watching, where he was about to test his new invention, the Teleporter, with the help from his large assistant Torbo. The result is a success, and the TV scientist declares that he will use his invention to teleport himself to anywhere in the world, but Torbo points out that he would have to take one of the teleportation devices there first, because he would already be there if he didn't, and it would render the whole thing useless. At that point, the TV scientist threatens to cut off Torbo's tongue again. This served as an inspiration for Phineas and Ferb to built on their invention in the episode. ("Does This Duckbill Make Me Look Fat?")
Though it may appear that the TV scientist is a fictional character in his early appearances ("Does This Duckbill Make Me Look Fat?, "Hide and Seek"), he would go on to serve as a member of L.O.V.E.M.U.F.F.I.N., which may indicate that he may be real at some point. During the L.O.V.E.M.U.F.F.I.N Pageant of Evil, he is seen presenting out a height limit chart with another evil scientist that disqualifies Dr. Diminutive from the contest because of his short height. ("Bullseye!")
He is later seen attending the L.O.V.E.M.U.F.F.I.N. Summer Stock Festival Play, where he is seen applauding for Heinz Doofenshmirtz's fantastic entrance along with the rest of the audience. ("Road to Danville") Later on, he is one of the few scientists attending the L.O.V.E.M.U.F.I.N. First Annual Disservice Awards hosted by Doofenshmirtz in the Knights of Danville Hall, but it was interrupted by the noise that the O.W.C.A animal agents are making in the other room, which resulted a fight between the agents and villains. The TV scientist later appears again helping out catching many of O.W.C.A.'s agents after the members of L.O.V.E.M.U.F.F.I.N learned that Doofenshmirtz had successfully moved the Earth away from the Sun to an early autumn, as part of Rodney's plan to rule the world. However, later on, the agents were freed and engage into another fight with the villains, but it wasn't until Dr. Diminutive pointed out that it's exactly the same brawl back in the ballroom. Realizing this, the TV scientist suggested that they leave, and all of the villains do so at once. ("Phineas and Ferb Save Summer")
In the episode Robot Rodeo, there is a scientist who looks almost exactly the same as this scientist, except for the fact that he is blond and wears white instead of black.