Warren Ampersand, also known as the Shape-shifter, is a creature seen in "Joshua and Margaret Investigations." He is a shapeshifting being apparently from an alien world or another dimension that infected Joshua with his venom, causing Joshua to develop a large boil on his head from which Jake emerged. Warren is, technically, 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, or at least when it was not in his "homeworld." In "The First Investigation," Jake watches his birth and sees that Joshua is his "mother" while Margaret is his adoptive mother. At the end, he meets the shape-shifter who he is surprised to meet and goes with it to his "homeworld."
Jake formally meets him at the end of "The First Investigation." 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 honor 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 a greyish 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 its 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," they finally get to meet and we see what kind of guy Warren really is. Warren starts off cheerful and seems like he is trying to get together with his son assuming he is the chosen one to save his homeworld. This turns out to not be the case at all. It turns out he is a horrible father who used his past sons' powers to make himself younger again. Even when he tries to suddenly change to be more empathetic, it turns out he is just trying to get on Jake's side to give him more power. He even was going to go to earth to consume the power and strength of his grandkids. Jake threw him in a black hole to protect his kids even if it meant he would be kept in space.
He can manipulate its body into any shape or size and has stretchy powers like Jake but uses them in a much more fluid fashion. He can shapeshift into multiple creatures like a baby, humanoids, a cat, owl, and even a planet among other unknown forms. Warren Ampersand can also change into a glyph-like shape and shoot beams of energy from his many eye stalks to open a portal to another dimension which resembles a dark blue lava lamp. He can also reproduce by impregnating other organisms by biting them if Warren deems them compatible (in Joshua's case, he was bitten on the head). Warren is shown to have much more advanced stretching abilities compared to Jake, being able to construct entire planets and beings without being physically connected to them.
- 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.
- He is also unaware of his great-grandchildren.