Warren Ampersand is a recurring antagonist in the Adventure Time TV series, who serves as the secondary antagonist of Season 9. He is also Jake's other dad who gave him his stretchy powers.
He was originally voiced by John DiMaggio, and is currently voiced by Dave Foley.
He first appeared in a flashback in the episode "Joshua and Margret Investigations." After Jake's parents Joshua and Margret go to Tree Truck's house to investigate a strange creature she saw. They find Warren in the forest in the form of an owl. He then bites Joshua on the head which makes him ill. Margret then goes off to cure Joshua by getting some venom from Warren himself. After she does Warren laughs manically before opening a portal to return to his home world. While he was gone the illness he gave to Joshua cause him to give birth to Jake out of his head.
He makes a cameo appearance in Jake's dream in the episode "Orb" foreshadowing Jake taking on his true form as Warren's son. He then makes another cameo in "Abstract" within another one of Jake's dreams. In the end Jake accepts his new change then reverts back to his old self.
He makes another appearance in "First Investigation" watching Finn with baby Jake from outside Joshua and Margaret's old headquarters. He then appears near the end where he appears old and weak, then he changes Jake blue again and tells him that they have to leave. He then opens a portal back to his home world then the two disappear.
His final appearance was in "Jake the Starchild" where he introduces himself as Jake's other dad and takes to his home planet where all the citizens are glad to meet him. Warren reveals that he's been watching Jake his whole life and that he's dying. He also tell Jake that he is needed for a prophecy that can save his home world. During a party Warren gives Jake a belt to match one Warren got for himself. After Jake starts stretching a lot he starts to get older and weaker while Warren starts to get younger and healthier. Warren then reveals that he uses the belts to steal Jake's youth so he could live forever, which is what he's been doing to all of his other offspring for years. Jake later tricks Warren into hugging him so he can switch the belts and make Warren stretch so Jake can regain his youth. When Jake reveals he has pups, Warren decides to go after them and steal their youth too. He climbs into a rocket ship and reveals that the whole planet and it's people were one big illusion. Jake however, grabs the rocket and throws Warren into a black hole killing him.
- Jake Jr.'s mouth is similar to Warren Ampersand's mouth, meaning that it is possibly a gene passed down from Warren, to Jake, then to Jake Jr.
- Andy Ristaino responded to a fan on Tumblr claiming that they were jokingly calling him "The Peeper."
- Warren appears to have died by being absorbed by a black hole, although his final words "I'm going 4D, baby" may indicate that he has ascended into a new reality.
- Warren Ampersand is named after writer Julia Pott's fictional high school boyfriend.