Kevin 11 is a mutant who could absorb energy. He first met Ben in a video games room until a group of bullies came and wanted to beat up Kevin. Ben scares away the bullies as XLR8. Kevin soon finds out about Ben and the Omnitrix and decides to make friends with Ben. Kevin in fact wanted to use Ben to commit crimes. Ben later discovers that Kevin is a sociopath and tries to stop Kevin as Fourarms. Kevin fights back and absorbs all the electricity in the area. Kevin jumps onto Fourarms and tries to suck all of the energy from the Omnitrix. Kevin then transforms into a half human and Heatblast creature. Ben still manages to defeat him.
Kevin soon gains absolute control over his new powers. He was able to transform into Stinkfly, Upgrade, Grey Matter, Fourarms, Ripjaws, Wildmutt, Heatblast, Ghostfreak, XLR8 and Diamondhead. However there’s a down side, he cannot stay his human form for a long period of time. Kevin blamed Ben for turning him into an abomination and sought revenge. He tracks down Ben and defeats Ben with ease in the beginning. Later Lt. Steel had been ordered to stop the aliens at any cost. At first, Lt. Steel suspects Ben is behind all of the crimes, but he soon discovers that Kevin is behind all of the crimes. Ben fights Kevin on a bridge, Ben uses Fourarms to stop Kevin and successfully defeats Kevin. Kevin wanted Ben to keep on fighting him but Ben refused. Ben told Kevin that he wasn’t worth his time, and an enraged Kevin transforms himself into all of the ten of Ben’s aliens from the Omnitrix. However, Kevin still loses and Ben knocks him into the water. And Kevin is believed to be dead, because (as Gwen points out) No one could survive that.
Kevin resurfaces later on and fights Ben on a wind farm. Ben was not faring well in this fight. Kevin then claims that he is 10 times as more powerful as Ben. They were teleported on to a Megacruiser by Slix Vigma, a creature that collects aliens from across the Universe to battle in a arena fight. Kevin and Ben decide to ally themselves and fight against Vigma's men. They soon discover that Vigma is a robot and Ben turns into Upgrade and takes him over. Kevin kills Vigma and tries to kill Ben but is thwarted by an alien that Ben saved in the arena, and Kevin is once again thwarted to defeat Ben..
Kevin gains control over the Megacrusier and forms an alliance with Vilgax, and both of them attack Ben. Ben had played with the Omnitrix and figured out the master code, he could now turn into any alien he wanted to, and he could stay in that alien form longer than 10 minutes. Vilgax figures that Kevin has the energy signature of the Omnitrix and he had the technology to remove the Omnitrix from Ben’s wrist. Before they can succeed Ben sets the Omnitrix back the way it was, now it Times out and he can only change for a little. Max uses the Null Void projector and sends Vilgax and Kevin into the Null Void. Kevin and Vilgax both fought each other for the Omnitrix and ended up being trapped there.
In a possible future, Kevin's future son, Devlin, befriends Ben's son Ken. Devlin could transform into his fathers original alien form and could easily change back to human. Devlin liberates Kevin. Kevin attacks Ben and Ken but Devlin betrays Kevin and helps Ben and Ken. Kevin was defeated again and was sent back to the Null Void and Devlin was adopted by the Tennysons.
Ben 10 Alien Force
In Ben 10 alien force Kevin somehow has broken out of the Null void and invested himself in some shady dealings involving level 5 alien tech which could very well put the earth in danger. It is when Magister saved his life that Kevin decided to help the heroes, that and the now 15 year old Gwen Tennyson might have swayed him to the side of good.
The Older Kevin's powers have also advanced, he now can absorb from any material and use it as a body armor. He has to be around enough of the substance in order to absorb it, otherwise he is just going to have only a small portion of his body changed. Kevin also reveals that his father was a plumber as well and he himself has always wanted to be one. Kevin's powers might have come from his alien lineage, like many others. He has been a great ally of the Tennyson’s, helping them find DNAlien dealings. He still likes to pick on Ben and give him a hard time. Kevin and Gwen show signs of a relationship, as Gwen asked Kevin to a dance. Kevin was even asking Ben for dating advice. Kevin helps Ben and Gwen defeat the DNAlien swarm.
Kevin accidentally absorbed a feedback pulse from the Omnitrix when Ben was screwing around with it and he was once again locked in an alien form, this time he became a living combination of different elements. Kevin hated this form, he thought himself to be a monster again. Kevin finds out an alien named Ragnarok killed his father and this drives Kevin to seek revenge. Kevin eventually ends up killing Ragnarok avenging his father's death. Kevin aids Ben in his fight with Vilgax and when Ben's omnitrix was destroyed, Kevin was restored to normal.
Kevin in Ultimate Alien has finally become full friends with Ben and established a full relationship with Gwen, he even shows a developing friendship with Grandpa Max. Kevin has become a fully certified Plumber. A lot of Kevin's back story takes place showing how he escaped the Null void, learning to control his powers and so on. A new villain has surfaced named Aggregor who is a fellow Osmosian like Kevin. Kevin helps Ben try and stop Aggregor from capturing run away prisoners that Aggregor imprisoned though Aggregor eventually succeeds and absorbs the aliens' powers. When Aggregor eventually enters the forge of creation, the team is defeated, it isn't until Kevin as a last resort absorbs the energy of the Ultimatrix to become powerful enough to stop Aggregor. Kevin defeats Aggregor and absorbs his energy returning him to normal, this however turns Kevin insane and he sets out on his old quest for power.
As Ultimate Kevin, Kevin tries settling old scores. He attacks the old Null void prison looking to get revenge as one of the inmates took up a father like roll teaching Kevin how to use his powers better and returning to his human form was killed. Kevin sought to kill Argit for all the times he double crossed Kevin. Kevin eventually eventually seeks out to destroy Ben. Him and Ben fight but Ben ultimately defeats Kevin and with Darkstar and Cooper's help, Ben and Gwen then absorb the excess energy Kevin returning him to normal.
Kevin is currently back to normal helping Ben and Gwen on random missions but a new threat in the name of Old George the original forever knight. Recently when a few of Ben's ultimates went Rogue, Kevin went to Azmuth on his planet in an attempt to save Ben who was sucked into the Ultimatrix, Kevin was fighting the guard but pleading to Azmuth outside of his building and Azmuth stated Kevin is evolving showing Kevin's growth from a punk kid to becoming a true hero.
Vilgax has returned surviving the incident in Alien Force, and has been taken in as a giant squid at a circus. A new group of enemies called the Esoterica mistaken him for a god, and Kevin and the gang attack the Esoterica in attempt to stop Vilgax. The team leaves, but they threaten he better watch himself. The real false god (who is really an ancient dragon) named Dagon promised Vilgax to restore his power but is tricked. Old George reclaims his old power and Kevin and the team try to stop George but fail. Kevin will be ready to fight Dagon with Ben and Gwen in case George fails.
Kevin helps Gwen and Ben try to save Charmcaster who has taken over Ledger Domain. Charmcaster eventually falls for Michael Morningstar who uses her magic for his own power lust. He is soon found out and defeated by Charmcaster.
Powers and Abilities
Kevin is an alien-human hybrid called an Osmosian. His primary power is to absorb energy and the matter of any object he touches. Kevin must have a decent amount of the substance when absorbing it to completely cover his body. When he absorbs energy he can shoot it as energy blasts and enhance his strengths. He can manipulate machinery such as turning it on, overloading and so on upon physical contact. When Kevin absorbs too much raw energy, it seems to drive him insane such as when he absorbed the energies of the Omnitrix and the Ultimatrix which also explained why he was a villain in the original series. When he absorbs too much energy like the Omnitrix at once, Kevin has usually been locked in that form. These instances of getting locked in alien form, have made Kevin weary of absorbing straight energy.
When he absorbs matter it covers his body thus he gains the property of said material. For example when he absorbed the properties of a tire, it allowed him to bounce around. It was noted by McDuffie that Kevin can absorb liquids and gain their properties. If he absorbed water for example, then objects would pass through him. Originally, it seemed when Kevin absorbed the material, it served as a second skin, but as his powers further developed the power seems to run deeper. He has had a hole blasted in him and absorbed metal to cover the hole and had his hand cut off while transformed and he regenerated a new one. Kevin has shown to absorb multiple items at once. He has shown that he can shape the material he absorbs into various weapons like forming his hands into hammers, swords, maces, etc. Kevin can fuse both hands together to also form a weapon or just grow his hands to an even bigger size. Kevin's control has reached a point he can form other objects than just weapons such as using his shape shifting powers to make a putter at a game of mini golf or make a key with his finger to pick locks.
Kevin can reverse the absorption process by releasing the absorbed material in different states. He can release the absorbed matter into a liquid state to repair holes and cracks or he can shape the material into items for someone like a helmet to protect someone. Kevin must have a large enough amount of the object he is absorbing to cover his whole body, otherwise it only covers part such as his hand. It has been shown Kevin can get tired when in armored form. When Kevin is knocked out, he loses whatever material he had previously absorbed and reverts back to his human form.
Aside from his main powers, Kevin possesses super strength which also depends on his substances absorbed. He has shown to throw around large machinery, take an Eiffel tower replica just a bit taller than he is and throwing it like a spear into a Techadon robot, killing it, hitting Ultimate Humongosaur a few hundred feet with a car and stopping his speeding car when the breaks were ripped out by slamming his legs through the floor and digging them into the ground all the while going down a hill. Kevin also has enhanced durability which increases depending on the substance absorbed. Such examples are getting hit through stone walls and taking Michael Morningstar's energy blasts and regularly getting hit by super strong opponents. Though not very book smart, Kevin is extremely intelligent when it comes to mechanics and repairing vehicles and he can identify most alien tech weaponry which he learned through studying in the Null Void zone. Kevin is a capable fighter and adapt in the use of various alien tech and firearms and he is a capable detective. Kevin is also an expert driver and pilot normally as he is normally the driver of the ships and in Alien Force the main source of transportation. Since Ben acquired his own car, Kevin and Ben seem to exchange rolls if taking one car which Kevin on occasion has complained about.
In the beginning Kevin was a street rat and major villain to Ben. He was driven insane due to draining energy and upon breaking out of the Null Void zone and encountering Ben and Gwen years later, Kevin was much calmer yet still arrogant. As he joined the group he eventually opened up them. He became best friends with Ben and fell in love with Gwen and the two eventually became a primary couple on the show. As Ultimate Alien progressed, Kevin has grown up a lot. Sacrificing his humanity to save his friends, Kevin once again absorbed the Ultimatrix to protect them and defeat Aggregor. Eventually Kevin was reverted to normal. When Ben was trapped in the Ultimatrix his life was in danger, Kevin went to Azmuth's planet and battled the security robot. While getting battered and beaten around, Kevin pleaded to Azmuth to save his friend. Azmuth pointed out Kevin has gone from a delinquent to a true hero. Kevin has grown up. He has given Ben dating advice and says somethings that the team needs to hear when the moment calls for it. While Kevin has grown up, he still acts immature at times with a crude sense of humor.