Kevin's physical appearance has changed from a 11 year old to a 17 year old. However, he retains some recurring characteristics, such as shoulder-length black hair, somewhat pale skin, and dark brown eyes.
As a kid, Kevin wears a black T-shirt, black arm bands, brown, blue or grey pants, all-black or black-and-red shoes, and a padlock necklace.
As a teenager, Kevin generally wears a black T-shirt, blue pants, and black shoes, and has his hair styled into a choppy mullet. He alternatively wears a white shirt, a blue short-sleeved jacket, blue pants, and black shoes.
Prior to moving out of Bellwood, Kevin's prominent outfit consisted of a black shirt, a long sleeved grey shirt, and blue holsters. He also wore a padlock necklace similar to the one he wore when he was younger, but marked with an "11". During his sequent visits, Kevin gains a few chin whiskers, some stripes on his gray shirt, and a cross-shaped scar on his chin.
As "Pyronite Kevin", Kevin's left arm and lower body remained unaltered whereas his upper right chest, head, and right arm was changed to that of a Pyronite.
As "Tetramand Kevin", Kevin's hair remained unaltered through he he gained red skin, crooked teeth, and large arms with black fingernails.
Kevin's first major mutation, dubbed "Kevin 11", mostly resembled a Tetramand, but with reddish-pink skin, a Pyronite-like upper left arm, a Petrosapien-like upper right arm, and Vulpimancer-like lower arms. He had Lepidopterran wings, a Kineceleran tail, an Ectonurite eye track on his chest, and an upper back resembling a Galvanic Mechamorph. His head consisted of Kevin's hair and ears, two left eyes similar to those of a Tetramand, a Galvan-like right eye, and the lure, teeth, and gills of a Piscciss Volann. He originally wore cargo pants but switched into jeans prior to meeting Kwarrel.
12-year-old Kevin's mutation was similar to, yet different from Kevin 11. His face retained Kevin's structure and hair, but had skin colored in two different tones of green, a Loboan-like right eye, an Opticoid-like left eye, a Gourmand- like mouth, and a head fin and eyes on his chin similar to that of a To'kustar. His body mostly resembled an Arburian Pelarota's, but with a Polar Manzardill's back and fins, a Splixson's lower chest and sensory nodes, Thep Khufan bandages, and Transylian shoulders. His arms had lower parts resembling an Arburian Pelarota's and upper parts resembling a Transylian's with red Opticoid eyes, small spikes, and fingers resembling Florauna tentacles. He also had Splixson legs, Florauna eggplant bombs, and a large Gourmand tail. He wore Kevin's pants and a Thep Khufan crown.
15-year-old Kevin's mutation retained his original frame but instead had his body made out of common elements. The right half of his face, the left half of his chest, the upper right half of his chest, part of his back, and his left arm were made of concrete, the lower right half of his chest, part of his back, his stomach, and his right arm were made of metal, the left half of his face was made of Taydenite, and his legs were made of wood.
As Ultimate Kevin, his composition was more complex than his earlier mutations from his youth. His face mostly resembled an Aerophibian's, but with Kevin's hair, a patch around the right eye colored like a Methanosian, a right eyebrow resembling a Vaxasaurian, and a jaw similar to that of an Evolved Arachnichimp but with an interior resembling that of a Sonorosian. His torso resembled a Vaxasaurian's, but the backside was colored like an Aerophibian and had a set of Necrofriggian wings. His right arm mostly resembled a Petrosapien's, but with two Crystalsapien crystal spikes on the shoulder and a Biot-savartian-like claw. His left arm mostly resembled a Methanosian's, but with a Biovosortian spike on the shoulder and Appoplexian-like claws. He had an Aerophibian-like right foot and an Appoplexian-like left foot. He also had a Vaxasaurian tail, two Cerebrocrustacean legs in place of a secondary left arm, a secondary right arm resembling an Arachnichimp's, and Orishan water ports.
17-year-old Kevin's mutation had a face resembling that of a Gimlinopithecus, but with red eyes, Kevin's hair, a Vladat-like mouth, a crest resembling both a Gimlinopithecus and an Insectoid, and Conductoid antennae. He had an upper right arm resembling a Segmentasapien's, an upper left arm resembling a Galilean's, a lower right arm resembling a Pturbosaurian's, and a lower left arm resembling an Atrocian's but with sharper claws. His torso mostly resembled a Gimlinopithecus's, with pieces of both Segmentasapien and Galilean near the shoulders. He had an uneven set of wings, with the left wing resembling a Nemuina's and the right wing resembling a Pturbosaurian's, and Orthopterran legs. He wore pants resembling Kevin's Rooter uniform.
Monster Kevin, an alternate version of Kevin 11, had a head resembling Kevin's but with a goatee resembling Quad Smack's and a mane resembling Bashmouth's. He had purple skin and a torso resembling Quad Smack's but with six arms rather than four. His upper left arm resembled Crystalfist's, while his upper right arm was a purple version of Hot Shot's. His middle left arm resembled Thornblade's while his middle right arm was a purple version of Bootleg's. His lower left arm resembled Undertow's, while his lower right arm resembled Dark Matter's. He also had Wreckingbolt's back, purple versions of Skunkmoth's wings, and Rush's tail in place of legs.
Powers and abilities
In the Prime Timeline, Kevin is an Osmosian capable of absorbing energy, matter, and DNA. His powers were believed to be either an unexplained mutation or alien heritage, but this later explained to be of a unique genetic component.
Kevin has the ability to absorb the energy and matter of anything (excluding certain materials) through his body at will and utilize it in various ways. If he is not absorbing excessive amounts of matter or biology directly into his body, he becomes wrapped in a coating that leaves his clothes intact. However, if he is wearing a Plumber Suit, the suit will not remain intact.
Kevin as undergone multiple mutations, most of which involved using his powers on the Omnitrix. Each Omnitrix-related mutation results in Kevin temporarily gaining the natural abilities of each species present.
In an alternate timeline, Kevin is an ordinary human equipped with a replica of the Omnitrix called the Antitrix that he generally uses to fight Ben out of pride and jealousy. Similar to the Prime Timeline Kevin's mutations, the Antitrix aliens are "cross-contaminated" hybrids.
If Kevin were to fight Ben 23, Quad Smack would be stronger and powerful than Handy Man based on his alterations to the Antitrix.
While Kevin can absorb all sorts of compatible matter, he cannot take too much of it. Such as with the Omnitrix, where he became mentally unstable and lost all accounts of control from all the DNA given to him. However, Kevin has recently overcome this weakness by mastering his powers.
12-year-old Mutant Kevin can be incapacitated by quills fired by Argit's Species.
Ultimate Kevin was sensitive to high-pitched noises, such as those produced by an Evolved Sonorosian.
When Kevin first appeared, he quickly became one of Ben Tennyson's most notable enemies, though he reformed by age 16.
- In the original continuity, Kevin's padlock was a spoil from the first crime he committed as a child which was stealing a bike and using it to run away from Bellwood to New York City.
- In the reboot continuity, the padlock contained a tracker that was placed there by the Forever Knight before Kevin destroyed it in the episode "Franken Fight".
- The idea of Kevin having his own Omnitrix in the reboot was a repurposing of an unused concept intended for the original series.
- During the original series, Kevin was initially portrayed as being a mutant. In Alien Force, he was changed to being a human/Osmosian-hybrid who inherited his powers from his biological father Devin Levin. However, in Omniverse, Osmosians were revealed to be a subspecies of mutant humans.
- The decision to change Kevin from an alien hybrid into a human mutant was because the crew wanted Osmosians to be more in line with his portrayal in the original series. Additionally, they did not want every aspect of Ben 10 lore to be derived from aliens.
- Kevin was the first non-Tennyson family member that Ben shared his secret (i.e. the Omnitrix) with.
- Kevin got this X-shaped scar due to being whipped by Swampfire. His counterpart in Ben 10,000's timeline also has a scar of the same shape.
- As the Antitrix aliens have been confirmed to be "cross-contaminated" hybrids, Monster Kevin is technically comprised of 23 different species, including human, Tetramand, Pyronite, Kinecerlan, Subsapien, Arburian Pelarota, Galvanic Mechamorph, Galvan, Cascan, Florauna, Lepidopterran, and Bashmouth's Species.
- Due to some of Monster Kevin's body parts having a more purplish coloration, Bootleg's arm resembled Upgrade's arm.
- Monster Kevin is inspired by both Kevin 11 and 12-year-old Mutant Kevin from the original continuity.
- The reboot version of Kevin shares many similarities with Albedo from the original continuity.
- Kevin and Charmcaster were created as foils to Ben and Gwen based around their youths. If Gwen received a spinoff series, Charmcaster would have joined her side just like Kevin joined Ben's side in Alien Force.
- At the end of Weapon XI Part 1, Kevin wore these clothes that were the same ones his future self wore in the original series.
- According to Dwayne McDuffie
- According to Duncan Rouleau
- According to the trivia version of the episode "Kevin 11"
- According to Kevin 11's lenticular bio card from Bandai's Ben 10 toyline
- According to Derrick J. Wyatt