- Tara Strong - Ben 10 and Ben 10: Omniverse (4 years old in "Don't Drink The Water" and then 10 and 11 years old)
- Fred Tatasciore - Ben 10 (30 years old Ben in "Ben 10,000" due to an alternate timeline)
- Yuri Lowenthal - Ben 10: Alien Force, Ben 10: Ultimate Alien and Ben 10: Omniverse (15 and 16 years old)
- Sean Donnellan - Ben 10: Ultimate Alien (36 years old in "Ben 10,000 Returns")
- Judd Nelson - Ben 10: Omniverse (36 years old in "Ben Again")
Benjamin "Ben" Kirby Tennyson (later known as Ben 10) is the main protagonist of the series. He is a 10-year-old (15 in Alien Force and 16 in Ultimate Alien and Omniverse) child from Bellwood, who found the Omnitrix during his summer vacation with his grandfather Max and his cousin Gwen. The watch-like device fastens on his wrist and gives him the powers and abilities to become a superhero which he uses to defeat evil while trying to escape the alien warlord Vilgax, who pursues him relentlessly in order to retrieve the Omnitrix.
For most of the series, Ben is portrayed as an immature, self-centered boy. In the beginning of the show, he only helped people with for the benefit of feeling like a hero. This leads Gwen, Max, and the others to doubt Ben and they wonder if he has what it takes to be a hero and if he should be the one wielding the power of the Omnitrix. Through the series, Ben matures dramatically and becomes a very capable leader in the sequel Ben 10: Alien Force due to Grandpa Max's disappearance and the threat of the Highbreed Invasion. However, he tends to relax into old habits during the third season.
Despite his immaturity, Ben's actions are motivated above all by a strong and sincere will to help other people; he'll stop at nothing to protect his family or anyone in danger. Sometimes, his idealistic nature tends to make him act naive. Though often thought of by many other characters to be quite unintelligent, Ben actually proves to be resourceful and cunning when needed, usually showing good adaptation skills when the Omnitrix doesn't provide him with the form he originally wanted. In the episode "Where the Magic Happens", Kevin is surprised when Ben is able to memorize a sentence of magic symbols with a mere look. Gwen also states that he isn't working to his potential in school, to which he agrees. While attending the Plumber Academy, Ben seemingly does not pay attention to his classes or the drill sergeant, yet still achieves a grade of 95 upon completion of the course. During the Academy, he was unable to handle the training as a human so he uses the Ultimatrix to get him through the training despite his drill sergeant telling him not to use it. How much of that is the previous training Ben received from his grandfather and his actions in the episode are unknown.
At some point between the two shows, Ben had removed the Omnitrix, spending some years without it, because he chose to give up from his superhero career to have a normal life, though he kept the Omnitrix as a souvenir, however, Ben found out that his Grandpa Max had mysteriously disappeared while investigating what Magister Labrid calls "an alien conspiracy with Earth in the middle" leaving only an enigmatic holographic message for Ben. Despite Gwen's doubts, Ben decided to use the Omnitrix again in order to find Max. When he toned down his immaturity in the first seasons of Ben 10: Alien Force, he proved to be a capable leader for his team, although after his success at saving the universe from the Hybrid Invasion, his overconfidence caused him to revert to his immature personality as well as a very competent fighter, and also Ben, Gwen an Kevin became "Deputized Plumbers". However, after his successful attempt at ending the Highbreed Conspiracy on Earth, Ben grew famous and was celebrated as a hero throughout the whole galaxy, now known as Ben 10, and received awards from various Alien ambassadors; this caused him to eventually relax and return to his immature attitude from the original series, with the addition of being somewhat cocky, much to Gwen's and Kevin's chagrin. To make it worse, Ben loses Azmuth's trust after a failed attempt to hack the Omnitrix.
Ben also discovers that he, his cousins Gwen and Ken, father Carl and Uncle Frank, have alien heritage, from a species called Anodite, though he doesn't have his grandmother's spark like Gwen. Although, in "Fame", it is shown that at the end of Ben's mission, his eyes turn pink noting that there might be a connection between him and his Anodite background. This is proven in "Ben 10,000 Returns" when he is able to conjure up an energy shield made of manna to block Eon's aging energy ray (though Gwen's powers are much more powerful).
In the two-part series finale of Ben 10: Alien Force, Ben lost the Omnitrix for Vilgax and was later forced to sacrifice it by ordering it to self-destruct. He then successfully took the Ultimatrix, a revamped version of the Omnitrix, from his evil twin Albedo. In addition to the original Omnitrix's shape shifting powers, the Ultimatrix gives Ben the power to turn into more powerful forms of his aliens, called "Ultimates."
In Ben 10: Ultimate Alien, Ben's secret identity is revealed to the world and he becomes a megastar superhero loved all over by kids. This series features Ben's new car that Kevin gave him for his 16th birthday in "Ben 10: Alien Swarm". Kevin says that he'll keep it (since Ben destroyed his own with Humungousaur), but Ben threatens to throw the new one if he can't keep it. Ben is seen frequently driving his new car, titled the "DX Mark 10" (shown as a Mazda RX-8 in "Alien Swarm") in Ben 10: Ultimate Alien.
- Meagan Smith - Ben 10 (10 years old)
- Ashley Johnson - Ben 10: Alien Force, Ben 10: Ultimate Alien (ages 15 and 16), and Ben 10: Omniverse (eleven and sixteen years old)
- Tara Strong - Ben 10 (30 and 42 years old in the episodes "Ben 10,000" and "Ken 10")
Gwendolyn Catherine "Gwen" Tennyson is Ben's 10-year-old (15 in Ben 10: Alien Force, 16 in Ben 10: Ultimate Alien and Ben 10: Omniverse) first cousin. She is also Kevin's girlfriend.
In the original series, Gwen shares a love-hate family relationship with Ben. Before discovering her dormant magical and Anodite powers, she helps Ben by simply using her innate cleverness and intelligence. She is known to be a capable gymnast and martial artist and has received a black belt in taekwondo. Gwen is a very good student, and in Ben 10: Omniverse, she is shown leaving for Ivy League College.
Overall, her most notable skill is her incredibly strong magical abilities. Having within her what Charmcaster calls a magical aura, Gwen is capable of using various magical artefacts, charms, talismans, spellbooks, and spells. On two occasions, Gwen has used the five Charms of Bezel to become a superheroine by the name of Lucky Girl. At first, her power and ability drew from the luck-granting Charm of Bezel, which innately gave her perfect luck. While wearing the charm, any action she took would result in a chain reaction benefiting her original intent, though oftem injuring Ben in the process. She later brought back her superheroine identity after obtaining the Keystone of Bezel, which greatly increased and strengthened her natural abilities to superhuman levels rather than just affecting her luck, and which granted her superhuman agility, stamina, and endurance. She was later forced to retire when the Charms of Bezel were again destroyed. However, in a twenty-year alternate future timeline, thirty-year-old Gwen had gone to the mystical interdimensional world of Bezel to receive a brand new set of mystical charms.
Five years later, in Ben 10: Alien Force, her magical abilities have greatly strengthened and she is easily able to control and manipulate energy from her magical aura to create energy blasts, shields, barriers, ropes, chains, stepping stones, and other weapons and items. Her paternal grandmother, Verdona, is a vastly powerful Anodite alien from the planet Anodyne; a free-spirited alien species who possess the ability to manipulate and control a supernatural force-like substance called manna (also referred to as life energy, chakra, or chi) which is the very lifeblood essence of all magic and life itself. Gwen is also able to take on an Anodite energy form just like her grandmother whenever she gets very angered, enraged or stressed. In the mystical world, Ledgerdomain, Gwen's magical and Anodite powers are tremendously supercharged and magnified.
Kevin Ethan LevinEdit
- Michael Reisz - Ben 10 (Season 1, 11 years old)
- Charlie Schlatter - Ben 10 (Season 2 and 4, with 11 and 43 years old in "Ken 10")
- Greg Cipes - Ben 10: Alien Force, Ben 10: Ultimate Alien and Ben 10: Omniverse (16 and 17 years old)
- Nathan Keyes - Ben 10: Alien Swarm
Kevin Ethan "Kev" Levin is an 11-year-old (16 in Ben 10: Alien Force, 17 in Ben 10: Ultimate Alien (through present)) Osmosian who first appeared in the series as one of Ben's enemies and later becoming a friend and ally. Believing his step father Harvey Hackett convinced his mom to abandon him after he accidentally destroyed his family's house when his powers first manifest, Kevin ended up living in the subway of New York City where he met Ben and used him to siphon the Omnitrix's energies to get back on those who demonized him. However, this has unforeseen consequences as Kevin was also infused with the DNA of the aliens that Ben has access to at the time. Combined with his later attempt to frame Ben, Kevin ended up becoming a chimeric hybrid of the alien forms. However, as later revealed, the stress of the transformation rendered Kevin psychotic and unstable.
Eventually, Kevin ends up in the Null Void where he manages to regain his normal form and master his abilities under the guidance of a fellow inmate before escaping and being found by the Rooters who train him while using his power to turn themselves and the Plumbers Kids into alien-hybrids for the organization's plan to assassinate Ben. But the attempt ends in failure and Kevin's memories altered to have no recollection of the Rooters and believe his father was an alien as he involved with the intergalactic black market. Despite lacking a proper formal education, Kevin possesses a vast scientific and technological knowledge of alien life and paraphernalia. While teaming up with Ben and Gwen during the Highbreed invasion of Earth, the false memories of his father influencing him, Kevin reconciles with Ben and, over time, becomes involve in a romantic relationship with Gwen. Kevin has a muscle car, based on a 1970's Dodge Challenger which is armed with Plumber and other alien technology.