Timothy was the teenaged fan of the Teenage Mutant Ninja Turtles who operated as an ersatz superhero under the name "The Pulverizer". After a mutagen mishap, he became the entity known as "Mutagen Man".
Timothy first saw the Turtles when they fought Baxter Stockman on the roof near his apartment. Thinking that the Turtles were crime-fighters in turtle costumes, he decided to become one himself. Making his own turtle costume and calling himself "The Pulverizer", he set out to become a hero, even though he had no fighting skills at all.
Months after seeing them for the first time, the Pulverizer finally meets the Turtles in person. When he attempts to stop the Purple Dragons, he is quickly outmatched and the Turtles come to his rescue. They succeed in saving his life, but his attempts to help them fight results in the gang escaping with their stolen loot. The Turtles try to ditch The Pulverizer, but the tails of his bandanna get caught in the door of The Shellraiser as they drive away. They unwittingly drive him back to the lair, but fortunately for them, he blacked out most of the way and didn't see how they got there.
Still oblivious to the fact that the Turtles are mutants (until Donnie tells him), as well as the fact that they don't want him in their lair, the Pulverizer quickly becomes a nuisance. He does, however, give them a clue as to what the Purple Dragons stole and why. However, they leave the Pulverizer behind with Donatello. After trying to ignore him for a while, Donnie tries to teach the overeager hero wannabe some basic self-defense moves with little success. In the middle of the training, after Donnie teaches him how to knock people over (where he fails horribly), Michelangelo calls and tells him about a situation with Raphael.
Donnie asks the Pulverizer to drive the Shellraiser while he makes an antidote for Fishface's venom. Before they reach the building, they reach a roadblock, which Donnie forces him to jump. After Donnie injects the antidote in Raph, he discovers the lead casing on the power cell is broken because of the jump. The turtles and Pulverizer get in the Shellraiser and try to hurry back to the lair. Unfortunately, the Kraang find them and the Turtles, except Leonardo, try to fend them off. Leo crashes the Shellraiser into a wall and he joins the action. Meanwhile, the Pulverizer stays inside the van and catches one of the Kraang stealing the power cell. He tries to stop it and fails, but he still pursues it. Donnie warns him not to go after the Kraang, but he ignores him. He tries to knock the Kraang down with a technique Donnie taught him, but he fails. Instead, two more Kraang droids attack him while the other one gets on a helicopter. At first, Donnie goes after the power cell, but he decides to help the Pulverizer. The Pulverizer blames himself for the power cell getting stolen, but Donnie admits it was his own fault. He then tells the Pulverizer that he won't be learning from him anymore, but Pulverizer vows to continue training.
He later joins the Foot Clan, but he is pathetic as a Foot Soldier, and is only kept in the ranks to work as cannon fodder. He tries to spy for his new clan, but is found by the Turtles. He reveals his new job to the Turtles with pride, much to Donatello's protest, but he also gives the Turtles some information about the Foot's plans. He then volunteers to be mutated in the clan, foolishly believing it'll make him a mutant hero like what happened to the turtles. Donatello comes in and attacks Dogpound and Fishface in order to save him. He is able to keep the Pulverizer away from the mutagen just as the other turtles arrive, who defeat all of the foot soldiers. When cornered by Dogpound, and with the turtles fighting the Foot soldiers and Fishface, The Pulverizer pours ooze on himself and mutates. He gets his wish to be a mutant, but turns into a hideous mess of organs, now unable to speak and barely sentient. When Dogpound locks the doors and rigs the place with plastic explosives, the turtles could easily leave, but Donatello refuses to leave without him. The Turtles store him in some sort of Mutagen Containment Barrel and Raphael breaks out with his stealth bike. At the lair, Donatello brings him to his personal laboratory and vows to find a way to cure him.
In The Mutation Situation, Donatello is running tests on Timothy's organs when the Kraang Communication Orb bursts into the lab and Donatello leaves to berate his brothers. Mikey later taps Timothy's barrel while Donatello translates a recent communication sent over the orb.
In Invasion of the Squirrelanoids, Timothy is seen in the background as the turtles examine a homeless man and see two squirrelanoids burst out of his mouth and watches the turtles struggle to catch them while the homeless man runs away. He later sees another two burst out of Raphael's mouth as the turtles struggle those two as well.
Donatello experiments with some mutagen, hoping to find a cure for Timothy and Kirby O'Neil. While experimenting, he explains to the contained mutant-Timothy about his heartbreak caused by April O'Neil, but when his experiment suddenly ends in failure and Splinter calls for Donnie, Timothy is left alone in the room. During this time, he stretches his newly gained tentacle-mouth to Donatello's lab-table and drinks some of the mutagen, resulting in Timothy evolving into a much more powerful mutant, with new arms and legs. He then goes on a rampage after April O' Neil, believing her to be the only one nice enough to be his friend from Donatello's stories. During a later battle, Mikey calls him "Mutagen Man" and during another battle later on, Mutagen Man also use that name to refer to himself. However, he is defeated in the end by Donnie freezing him by tricking him into drinking faulty retromutagen. Donnie still promises that he will try to make Timothy human again one day.
In The Invasion, Part 2, Donatello tells the frozen Timothy that they hope to return someday and that if they don't manage to do so, he would be unfrozen in approximately 70 years, hoping that the world will be a better place by then.
In The Creeping Doom, he makes a brief appearance in Donnie's lab.
As a human, he is an overweight teenager In a Turtle costume. He wore a rubber green suit with a yellow stomach area, with lines in it that resemble the turtle's. He also wore a red bandana similar to Raphael's. As a mutant, he is a transparent blob monster with his brain and other organs floating around inside of him. When consuming mutagen, yellow, blobby hands and legs sprout from the openings of his canister. Both arms and his right leg have silver, spiked wrist bands.
Overly-excitable, clumsy and a big dreamer, The Pulverizer doesn't seem that bright or fit to be a ninja or crime-fighter. He's determined to be a superhero, but his lack of patience, poor physical shape and naive worldview makes him more of a hindrance than anything else. The Pulverizer is overall oblivious to the ways of the ninja and is easily defeated by almost every opponent he faces, yet he stays optimistic in the faith that he is a great warrior. In "The Pulverizer Returns", he was working alongside The Foot Clan, however, it is implied that they too thought he was worthless - and that they only intended to use him for an experiment. Ultimately, believing that the highly dangerous, painful and unpredictable mutagen would transform him into a mutant superhero, despite the explicit warnings from Donatello, proved to be his undoing.
After the trauma of his mutation, he became even less intelligent than he already was and his demeanor devolved into becoming more feral and aggressive. However, he did momentarily seem to possess enough presence of mind to comprehend what happened to him after seeing his reflection, and could apparently recognize his own name. After being contained, he seemed pretty mindless.
In Mutagen Man Unleashed, he regains a small amount of intelligence, Donatello referring to him as a "Barely Sentient Glob of Intestinal Goo". After he grew some limbs from drinking mutagen, he became quite deranged and out of touch from reality. He also gains speech from the speaker Donnie built for him. Whether out of loneliness or the mutagen's effect, Donnie's talks (or rants) about April made him see a kindred spirit in April. He apparently blames the Turtles for what happened to him, and saw that April was the closest thing he could have to as a friend.
As the Pulverizer, he was an incredibly bad fighter, and the Foot Clan only found him useful for being a distraction of enemies.
As Mutagen Man he gained a lot more powers, including super strength (actually able to take on the Turtles in a fight), regenerative powers (able to regrow a severed hand a few moments after it was cut off) as well as acid leaking out of holes in his palms and fingers (the acid also shot out like blood after his hand was cut off). It is shown that he can use his mouth and "throat" like a tentacle outside of the glass cabin carrying his organs, able to eat and swallow mutagen, as well as lifting an opponent in battle. However, contrasting his new gained super powers, his mutation also resulting in him suffering from a serious weakness: his addiction to mutagen, in order to maintain the use of his limbs, otherwise they shrivel up and weaken greatly. Because of this, Donatello realized a way to defeat Mutagen Man - by using a certain chemical reaction in a mutagen canister, he successfully caused the mutant to freeze up entirely after ingesting it.
- The Pulverizer's costume resembles the design of the Turtles from 1987 TV series, including having his initial on his belt.
- His idolizing of the Turtles, and attempt to become like them, mirrors both Zach from the 1987 series and the second Turtle Titan from the 2003 TV series.
- His training with Donatello is similar to Casey Jones' with the turtles in the 2003 TV series.
- He is also the fourth human to be on friendly terms with the Turtles (the first being April O'Neil, the second being Mr. Murakami, the third being April's father Kirby O'Neil, and the fifth being Casey Jones).
- It is possible that Pulverizer is inspired by the popular comic book and movie character Kick-Ass, as both characters live in New York, both have no training and are often beaten up by criminals, and both are trained by a martial artist (Pulverizer by Donatello, Kick-Ass by Hit Girl). Also, they both are inspired by superheroes to become real-life superheroes.
- Pulverizer trained in Chris Bradford's Dojo in an attempt to follow Donatello's advice to get training.
- Despite his promise, Donatello never cured Timothy. While it's never explained why exactly, whenever Donatello had to create retromutagen, it was always for an urgent situation like trying to retromutate Kirby O'Neill, Karai and later Super Shredder. It's also possible that the retromutagen may not work in his frozen state.
- Once mutated, he did not become a traditional animal-hybrid mutant, likely because he did not touch any animals without his gloves on around the time he was exposed to the mutagen. Donatello and Dogpound did touch him prior to the mutation, but only on clothed parts of his body, it is unknown if any other human would turn into the same thing if they came in contact with the mutagen without having prior contact with an animal, plant or fungi.
- It Is possible that the mutagen did interact with a certain form of life: The microbes commonly found on and inside the human body. His mutant form can be compared to a single celled organism, with vital components suspended within a membrane.
- Laird is embossed on Mutagen Man's voice communicator. This is a tribute to Peter Laird, the co-creator of the Teenage Mutant Ninja Turtles franchise.
- "You forgot to pay for that, but I accept cash, checks, or TEETH!"
- "I wanna be a hero NOW!"
- "I don't usually drive over 8 miles per hour."
- "Check out these muscles. Foam Rubber! Much faster than working out!"
- (After doing one move semi-correctly) "All Right! When do I get my black belt?"
- "I don't have time for the basics, just skip to the good stuff!"
- (About Splinter) "Does he know he's a rat?"
- "OW!! OH, IT BURNS! I DIDN'T THINK IT WOULD HURT SO BAD! "
- "AH, OH!"
- "IT REALLY BURNS."
- "You can survive with just one kidney right?"
- "This is my chance to be like you guys! Pour some mutagen on me AND BOOM I'M A SUPERHERO!"
- "Dude, what's with all the pizza boxes!?"
- "OKAY Giant...Man Dog Thing.......you asked for it! MY MUTATION!"
- (To Leo) You were all like, "Let's Finish this!" (to Raph) And you were all like "You're going down!" (To Mikey) And you were all like "Bees!!" (to Donnie) "Oh, And you were like.......You were like the strong-silent type."
As Mutagen Man
- "Speaking to you, Donnie."
- "I like April, Donnie."
- "April friend?"
- "Where is April O'Neil?!"
- "Human, help find April!"
- "Po-lice! Help find April!"
- "Stupid humans hurt me?!"
- "AHH! You punk kid moron!"
- "Now, I crush you!"
- "Wait! April friend!"
- "No! Stop! April do come back!"
- "April, wait. Be good friends."
- "No! Must find April!"
- "Die, turtle..."
- "NO! April not turtle friend! April only my friend!"
- "Turtles hurt April! Hurt me! Must destroy Turtles!"
- "Ugh. Powering down."
- "April, I'm coming--"
- "Leave Mutagen Man alone!"
- "April is mine!"
- "AHH! Destroy you all!"
- "Turtles... gone?"
- "More mutagen!"
- "Donnie... Something's... wrong!"