Other main characters include secret agent Perry the Platypus (who is also Phineas and Ferb's pet) and the evil scientist Dr. Heinz Doofenshmirtz.
[2] On August 25, 2011, the series was renewed for a fourth season as part of a deal between Dan Povenmire, Jeff "Swampy" Marsh, and Disney, along with a feature film and possible spin-off.
[7] The episode "Doof 101" was intended as a backdoor pilot for a spin-off series that focused on Dr. Doofenshmirtz becoming a high school science teacher, but was not picked up.
Dr. Doofenshmirtz and Major Monogram have their hearts set on revealing the top 10 musical numbers from Seasons 2 and 3, but soon find out that celebrity host Kelly Osbourne has been brought in to fill the role.
Unwilling to submit to playing second fiddle, Doofenshmirtz makes it his mission to thwart Kelly until Perry the Platypus sets out to stop his nemesis from ruining the entire show.
Dr. Doofenshmirtz gets punished with community service for being evil, and he is forced to be a science teacher at Danville High School, much to his daughter Vanessa's dismay.