Sunder

Sunder is an alien bounty hunter that first appeared in the episode Single-Handed.

Ben 10: Alien Force
He was sent by Vilgax to pursue Ben and to try to remove the Omnitrix from Ben by using his energy axe to bring to his master. The result inadvertently sent Ben to the Null Void, but only left Ben's left hand on Earth, where the hand itself managed to escape from Sunder and knock him out before leaving to find help.

When the hand was found by Julie, she brought it to Gwen and Kevin. They fought to keep Ben's left hand from falling into Sunder's clutches. When Kevin invented a machine that could bring Ben back, it was a success except that Ben's left hand is now in the Null Void. As Sunder charged toward the group, Kevin activated the machine once again and restored Ben's left hand to his body. However, it also sent Sunder to the Void.

Ben 10: Ultimate Alien
Sunder returned in the first episode of Season 2, The Transmogrification of Eunice, where he was on a mission to retrieve the Unitrix, which has taken the form of a girl named Eunice. At first, Ben and his team thought Sunder wanted Eunice for himself, but at the end, it is revealed that Azmuth hired him to bring Eunice back to him in exchange for Sunder's release. Ben convinced Azmuth to let Eunice have a normal life and be one of his assistants as he always needed a helping hand tending Primus, as it needs some help and care. When Azmuth, Eunice, and Sunder left, Sunder asked to Azmuth if he is still getting paid even it failed.

Ben 10: Omniverse
Sunder is confirmed to return in the series. His axe is connected to a whip and his hair is bigger. He has spikes on his shoulders and knuckles.

Ben 10: Alien Force

 * Single-Handed (first appearance)

Ben 10: Ultimate Alien

 * The Transmogrification of Eunice (first re-appearance)

Ben 10: Omniverse

 * Have I Got a Deal for You (first re-appearance)

Video Games
Sunder appears in Ben 10 Ultimate Alien: Cosmic Destruction for all consoles. He appears in Paris, and tries to take the second piece of the Potis Altiare after Ben defeated the Vreedle Brothers. After two failed attempts on Ben's life, Sunder fights Ben on the Eiffel Tower, but is soundly defeated by Ultimate Swampfire and thrown off the tower.

Powers and Abilities
He has an axe which is able slice through things. It can also send whatever it slices to a different dimension when it strikes something such as the Prototype Omnitrix, as he was able to send Ben (minus his Omnitrix hand) to the Null Void. He also uses a Hover Board for transportation. He has many gadgets inside his hover board, and possesses superhuman strength sufficient enough to hold his own against Ultimate Cannonbolt, Kevin, Gwen and Eunice all at once. It is not known whether these gadgets are used for combat or sells them for profit. He is also shown to be durable, able to withstand repeated injuries such as being able to withstand Diamondhead's shards at point-blank to the face, though it still causes him discomfort.

In The Transmogrification of Eunice, he possess a powerful blaster-pistol which he reveals he obtained on Galvan Prime (and likely is of Galvan design given its power). Though not specifically stated, it is possible it was given to him by Azmuth to help him in his task of retrieving the Unitrix/Eunice (meaning it is possible that the weapon was designed or constructed by Azmuth himself, but it's not likely as Azmuth doesn't make weapons, so it was likely given to him from someone else as confirmed by Dwayne McDuffie ).

Trivia

 * He's similar to Red X in Teen Titans status wise as he is only looking out for himself and is neither a villain or a hero as show that he was fiercely chasing Ben in Single-Handed but didn't want anything to do with Ben in his next episode. It was only because Ben and his team interfered that he fought them similar to how Red X fights the Titans only when they interfere with his work.
 * He's another villain Ben has not defeated on his own. The others are Albedo and Aggregor.
 * Every episode or video game Sunder appears in Spidermonkey appears in.
 * He resembles Terrax from Marvel Comics.
 * He uses a Glider just like Green Goblin and The Hobgoblin characters from Marvel Comics. Someone mentioned this on Dwayne McDuffie's website and he said it "wasn't ever intentional".
 * His name could be a reference to the term "tossed asunder" or to the word sunder' meaning to part, separate, or divide (it should be note that Ben's hand was separated from his body by Sunder, meaning that Sunder's name could be references to this).
 * Dwayne McDuffie confirmed that he had worked for Vilgax to retrieve it.
 * He is one of Ben's most powerful enemies considering the fact that he was able to hold his own against Ben, Gwen and Kevin in both their battles. He also beat two ultimates.
 * Ironically, Azmuth (who is one of Ben's allies) had to hire Sunder, who is one of Ben's enemies.
 * Why Azmuth hired Sunder was due to certain circumstances since he knows very well Ben, Gwen, Kevin, or the Plumbers could do the job Azmuth designed but they are a police force and he has no authority over them. However it is likely that given his plan to de-activate the Unitrix/Eunice should it become active, Azmuth likely predicted that Ben (and by extension Gwen & Kevin) might object it (as he eventually did), hence his decision to hire Sunder.
 * Though he is a villain, he is willing to work for Azmuth (who is a good guy and a mentor to Ben), however due to his status as a bounty hunter, he is willing to work for anyone who pays him (be it an evil warlord like Vilgax or the heroic creator of the Omnitrix, Azmuth), thus this makes him a free agent. Sunder's willingness to work for Azmuth may also be due to Azmuth's being responsible for freeing him from the Null Void. Doing a job for Azmuth may be his way of repaying him for freeing him (however despite being in Azmuth's debt, he still expects to be paid for his services).
 * It is said by Dwayne McDuffie he was hired by Azmuth because he specializes in retrieving unique objects, and the Unitrix could have transformed into *any* sapient creature in the galaxy. Azmuth needed someone resourceful and tough. He is also considered the best.
 * Sunder is another word for "steal by any means necessary" which is a reference to his bounty hunting job.
 * He is voiced by Powers Boothe who is best known as Lt. Col. Andrew Tanner in Red Dawn, FBI Agent Wesley Doyle in Frailty, Senator Roark in Sin City, Col. Jim Faith in MacGruber, Cy Tolliver on Deadwood and Vice-President Noah Daniels on 24. Boothe is also known for his voice acting such as Leslie Hunt in The Looney Tunes Show, Gorilla Grodd in Justice League and Justice League Unlimited and Lex Luthor in Superman: Brainiac Attacks.
 * The form of his head, and his hair style resemble V.V Argost from Secret Saturdays.
 * He is voiced by David Kaye in Omniverse.