Kevin Levin (Classic)/Omniverse

Sometime after the events of Ultimate Alien, Kevin and Gwen left Bellwood, as Gwen went off to college, and Kevin found a home and a job near campus so he could be close with her, but not before chasing and taking down Zombozo together as a team one last time.
In Many Happy Returns, he asked Ben to hide him from Princess Looma and revealed that he fought, and defeated, her when he was 14 and to get an engine for his car. He ended up having to marry her in three years. This not only caused Gwen to become angered at keeping this secret (and giving Looma a decent thrashing), but Kevin kept quiet about the man who next defeated Looma would have to marry her; the end result was Ben getting engaged to her. Satisfied that one more thing from his past wouldn't be haunting him anymore, Kevin left with Gwen in his car, much to Ben's irritation, muttering "Kevin is so dead".
In Showdown: Part 2, he was later recruited, along with Gwen, to find Ben, who had vanished after destroying Pakmar's business again. He ended up on Galvan Mark II, where he prepared to help Ben fight Malware. However, he ended up having to fight off Khyber's former dog. During this scuffle, Kevin managed to tame it and learn its gender was female. Having taken a liking to Kevin over Khyber, the dog decided to stay with him instead. Kevin resumed his life as normal, but with a new pet to add to his responsibilities.
Kevin made another appearance in The Frogs of War: Part 2, along with Gwen, Rook, and Argit, being a part of the resistance force that was still going against the invading Incursean army. With the help of Ben, who managed to return in his new Incursean form Bullfrag, the team rescued Max along with Driba and Magister Patelliday and freed Earth from the Incurseans.
Kevin made a cameo in Mud is Thicker Than Water, in which Gwen told him and Rook to enjoy the auto show, and they drove off.
Kevin had a main appearance in the following episode, OTTO Motives. Kevin and Rook arrived at Khoros to attend the auto show. As they walked around, they soon crossed paths with Argit. While they thought he was up to no good, the three teamed up once they found Otto, saying that they waited 5 years to get their revenge. They headed towards him, but they were thwarted by Otto's Violet Offenders. They defeated Otto after a fight between Upgrade and Otto, who became merged with a series of cars to become a giant robot.
Kevin, Gwen, and Zed were seen in the Rustbucket 3 to save Ben and Rook in For a Few Brains More where they helped defeat Khyber and Albedo.
Kevin made an appearance in Mystery, Incorporeal, in which he arrived with Zed to Friedkin University. He eventually helped Ben to fight a Rock Monster, and to investigate who was behind the attacks of the monsters. Once the team found out that it was Darkstar's doing, Ben, Rook, Kevin, and Zed fought many obstacles, including a fully powered Morningstar. The team eventually stopped him with the help of Ben as Ghostfreak.
In The Rooters of All Evil, Kevin was seen at the garage where he was eventually visited by Ben who says a group called the Rooters are after him. Kevin was uncertain on who they were but believed he should call Gwen. The Rooters eventually showed up and Kevin bumped heads with the leader, Servantis, and remembered who he was. Kevin then escaped in his new car with Ben and decided to tell Ben what happened between him and the Rooters. Kevin said that Servantis messed with his memories and that he is a "bad guy" who is part of the Rooters. The Rooters themselves suddenly attacked his car and Kevin absorbed metal while Ben transformed into Ampfibian. However, he and Ben were quickly defeated by the Rooters and were taken back to Plumber Headquarters. It was revealed that Osmosians aren't really aliens but are just humans with alien abilities. It was also revealed that Osmosians have different abilities and Kevin's ability is to absorb matter. Servantis was also the one that named the Osmosians and Kevin said that Servantis needs him to make a hybrid army.
Shockingly, it was then revealed that Devin Levin isn't real and was just a false memory that Servantis implanted into Max so that he would keep watch over Kevin. The Rooters began to fight against Ben and the others, but Kevin escaped thanks to the distraction, and everyone believed he wouldn't be seen again. However, at the end of the episode, Kevin met up with Argit in Undertown and zapped him with the red energy, restoring his memories.
In Weapon XI: Part 1, Kevin went to Alan Albright's farm to get the young Plumber to go with him. However, Swift of the Rooters soon appeared and Alan didn't trust Kevin after he almost killed him in the past. Kevin absorbed some wood in order to battle with Swift but was nearly burned by Alan due to the latter still not trusting him. However, Kevin finally gained Alan's trust again after blocking a near fatal blast from Swift. Eventually, Swift was forced to retreat back to the Null Void after getting hit by Argit's quills and Kevin shocked Alan's head, restoring old memories. 
Kevin, at some point, had left a coded letter to Gwen saying he has got Alan and that she must get Manny and Helen but not tell Ben about it. Later, Kevin was with Alan and Argit, and Alan wanted to help Kevin out. However, Kevin shocked Alan again, triggering another flashback that showed Alan receiving his Pyronite powers. Kevin said he would go in alone into the Null Void to confront Servantis and asked Alan to take care of Zed. Kevin headed inside and eventually reached Rooter Headquarters. Servantis was hoping to take out the "coming storm" but Kevin lashed out, telling him to stop calling Ben that and Ben is his friend. Suddenly, Ben, Gwen, and the Amalgam Kids arrivec, much to the anger of Kevin. Servantis then put his plan into action by shocking the Amalgam Kids and turning them against Ben. Servantis then created a forcefield around himself and Kevin and seemingly convinced Kevin to turn on Ben. Kevin thrashed Ben around (who was Kickin' Hawk) until the latter was forced to retreat. At the end, Kevin rejoined the Rooters and decided to carry out his plan to destroy Ben.
In Weapon XI: Part 2, Kevin was seen with the Rooters where he was searching for Ben. Kevin was determined to kill Ben in honor of Pierce's name. Kevin was eventually confronted by Ben as Gutrot but quickly touched the Omnitrix and mutated again. Ben transformed into Swampfire but Kevin easily contained him. Eventually, Ben was caught by Helen, and Kevin took him to Servantis. When Ben woke up, it turned out that Servantis created a device that would destroy Ben and the Omnitrix at the same time. However, before Kevin could toss Ben inside, Kevin dropped Ben and picked up Servantis instead. Kevin then headbutted Servantis and shocked the rest of the Amalgam Kids, turning them back to normal. Kevin did that to stop Servantis from alternating the other's memories and turns back to normal, explaining it all to Ben. Kevin told Servantis that Ben is like a brother to him and that he will never turn on him again. Later, the Rooters were stripped of their Plumber status by the Magistrata and Kevin left the Null Void with everyone else.
In Charm School, Kevin was seen at Friedkin University working on his car. Gwen attempted to get him to come to see why Charmcaster was also at the University, but Kevin said Charmcaster was her problem. However, Kevin decided to go after hearing Ben was coming as his car may get destroyed again. Eventually, Ben and Rook arrived, and Kevin decided to use Rook's expertise in alien tech to help build the ultimate car that can survive anything. Kevin took Rook into a room with numerous advanced alien tech revealing he used his powers to harvest Taydenite in order to keep getting money (saying he doesn't have to work ever again). Eventually, Kevin and Rook constructed the perfect car capable of withstanding everything. However, when a magic spell from Gwen and Charmcaster's fight hit the car, it completely disappeared, much to Kevin's horror. However, Kevin got over it and helped Gwen and Ben fight off Charmcaster and her Stone Bats. Eventually, Charmcaster was defeated, and Kevin decided to go to the auto show with Rook.
In Third Time's a Charm, Kevin and Zed had taken residence in Lucky Girl's headquarters, still feeling sad about his car. Gwen said she had searched all over the universe for his car, but Kevin begged her to search once more. They landed themselves inside his car in Legerdomain, but Kevin got teleported out with his car, leaving Gwen stranded. Kevin called Ben and Rook for help as he was sure that Charmcaster was the one behind the situation. The three boys met Bezel, the most powerful sorcerer of all. In the library, Charmcaster appeared as she showed them that she had turned Gwen into a totem, much to Kevin's shock. The boys got teleported out and Charmcaster made a magic barrier that prevented them from entering the library. With the help of Bezel, they were able to access the library to fight Charmcaster and her Rock Monsters. Zed took the totems of Gwen, Darkstar, Hex, Addwaitya, and Bezel as Charmcaster turned into a dragon using a spell. Ben and Rook then covered Kevin as he ran to his car, but the attacked from his car would not work since he does not know magic. Ben managed to trick Charmcaster by having Skurd absorb Bezel's totem, telling Charmcaster to look inside her bag. Charmcaster touched the drawing that Gwen made using Charmcaster's magic from her lipstick, turning her into a totem and trapped inside her bag. Kevin was seen back in Lucky Girl's headquarters, being relieved that Gwen was safe and that she and Charmcaster can be friends under different circumstances.
At the end of A New Dawn, Ben called Gwen to get Kevin and proposed that Ben, Gwen, Rook, and Kevin all go on a road trip to explore the universe they watched being created together.