Warren Ampersand the Shape-shifter is a creature seen in "Joshua and Margaret Investigations." He is a shape-shifting extra-dimensional alien being that infected Joshua with his venom, causing Joshua to develop a large boil on his head from which Jake emerged. Warren technically is the biological parent of Jake, which Jake eventually learns later.
Tree Trunks mentioned to Joshua and Margaret that the creature had touched her and several other citizens of Ooo on the shoulder, and it cackled knowingly before opening a portal and returning to its homeworld, suggesting that it might have been seeking to create some sort of hybrid offspring on this world, the result of which was Jake. Warren resided in the Pantheon of Savings when he was not on his "homeworld."
Jake formally meets him at the end of "The First Investigation," during the time he witnesses his own birth. and learns that Joshua is his "mother", while Margaret is his adoptive mother. This continued into "Jake the Starchild," in which Warren introduced himself, and transported his son to his home world. Upon arriving there, Warren revealed to Jake that he was dying. Warren showed Jake a museum he made in his honour and revealed he had been watching over him for years. Jake later found out, that Warren had only brought him to his world to absorb Jake's powers, eventually killing Jake as he had done so with his many other offspring. By the end of the episode, Warren decided to do the same to Jake's children but was thwarted by Jake and thrown into a black hole.
Warren Ampersand is midnight blue in color when young and grey-blue when old. He has five separate yellow eyes with red pupils in the order of a star. The eyes change in number with each transformation as well as the shape of his body and legs. He possesses a circular mouth split in a varying amount of directions and many sharp teeth. He has the ability to change into what appears to be an owl, a cat, a baby, and many other unknown forms.
His personality is mysterious when Jake initially meets him. However, in "Jake the Starchild," his true personality is shown. Warren starts off cheerful, pretending that he is trying to reconnect with his son, even going so far as creating a museum in Jake's honor. This turns out to be a ploy to steal Jake's powers and make himself young again, as he has done with all of his offspring in the past. He's extremely manipulative, even attempting to appear empathetic in order to get on Jake's good side and gain the upper hand during their fight. Upon realizing his defeat by Jake and finding out about the existence of his grandchildren, his personality flipped again as he explained his plan to travel to Ooo and consume their power instead.
Warren is shown to have much more advanced stretching abilities compared to Jake. Just like Jake, he can manipulate his body into any creature, shape, or size. He also has stretchy powers but uses them in a much more advanced and fluid fashion. He is capable of shape-shifting at a much larger scale and higher complexity than Jake, at one point covering an entire planet and forming a civilization purely from his body. Warren can also change into a glyph-like shape and shoot beams of energy from his many eye stalks, opening a portal to a dimension which resembles a dark blue lava lamp. If Warren deems another organism compatible, he is able to impregnate them by biting and injecting them with his venom (in Joshua's case, he was bitten on the head).
- 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 it "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.
- Warren is similar to Martin Mertens, as both only sought to use their children for their own gain.
- Unlike Martin who actually helped his son, Warren did not redeem himself in his son's eyes.
- Warren mentions he had other unknown children, this would mean Jake had half-siblings.
- He also stated that Jake was the only one he felt guilty about draining.
- Until Jake showed him, Warren had no idea that he had grandchildren or any extended descendants.