Ragnarok

Ragnarok is a character introduced in season 3 of Ben 10: Alien Force. He is notable for being the one who murdered Devin Levin, Kevin's father.

Backstory
According to Max's flashback, Ragnarok was originally a powerful and dangerous alien criminal from unknown origin, who possessed a ship able to drain energy from suns, destroying them in the process (something reminiscent of the Fallen's plan in the movie "Transformers 2: Revenge of the Fallen"). As he was about to absorb Earth's sun, Devin Levin and Max Tennyson successfully stole the key for his device. Ragnarok succeeded in caught their ship, and threatened to kill Max if Devin wouldn't tell him where the key was. When Devin declined, Ragnarok attempted to kill Max, but Devin put himself between them, and was fatally wounded instead of Max. Furious, Max used the element of surprise to send Ragnarok in the Null Void, where he was taken in custody.

Ben 10: Alien Force
Ragnarok appeared in Vendetta, where he escaped from his Null Void prison and the Null Guardians and arrived on Earth. After he trashed Kevin's house in order to find his key, Kevin's mother revealed him what exactly happened to his father, causing the young Osmosian to start looking for Ragnarok in order to get revenge. Feeling worried for Kevin, Ben and Gwen learned exactly who Ragnarok was from Max, and attempted to help Kevin, only to be asked by him to stay out of his way. Eventually, Ragnarok got the key back, and attempted to use it to activate his machine, but Kevin successfully infiltrates his ship, and destroys the ship's command, causing the device to be damaged and the air tank to break open. Ragnarok then begs Kevin for help, stating that his father was a Plumber and would never have let him die. Instead, Kevin just took the key from him and left him be sucked into cold space, seemingly causing his death.

Ben 10: Ultimate Alien
It's currently unknown if Ragnarok will appear again, though Dwayne McDuffie stated he believed it would be a good idea.

Powers and Abilities

 * Superhuman Strength, Stamina, and Durability
 * Solar Energy Manipulation
 * Agility Ragnarock_face.jpg

Trivia

 * Ragnarok is the end of the universe in Norse Mythology, where the gods and giants will die and the universe will be reborn.
 * He is one of a few Ben 10 villains known to have commited murder/genocide (the others being Vilgax, Aggregor, Adwaita and Urian). Because he was responsible for killing Devin Levin, he is Kevin's sworn arch nemesis (basically he is Kevin's Vilgax, though darkstar may also be considered this, especially since Ragnarok is dead).
 * Though it is most likely just a coincidence he shares many physical characteristics with Doomsday of DC fame who at a time had coarse white hair and grey skin. It also may be noted that there names share the same meaning "the end of the world."
 * It is possible that Ragnarok and Sunder could be of the same alien species, as they both have white hair and gray skin and they both wear red and black clothes (that could just be a coincidence though).
 * Though his blast that hit Devin did kill him, he was not intentionally trying to kill him. He was trying to kill Max.
 * He is the first notable character to be killed (apparently) in cold blood by a main character of the show (any murders Kevin 11 in the original series that happened offscreen not applying of course).
 * When Kevin introduces himself he makes an oblique reference to the Princess Bride, saying "My name is Kevin Ethan Levin, you killed my father, prepare to die", echoing the famous quote of the book, "My name is Inigo Montoya, you killed my father prepare to die", (repeated). According to Dwayne Mrs' Levin had read the book to him as a child.