|Family||Dee Dee (sister)|
|First Appearance||Ego Trip|
|Voiced By||Jeff Bennett|
Action Dexter is Dexter's future self as an adult. He has big muscles and can fight like a man. He can operate and control weaponry which he uses to fight evil in the dark future where Overlord Mandark rules over the world.
Action Dexter is a big muscular man who has an orange beard and glasses. He wears a black shirt and a white ripped lab coat. It's revealed he has gone bald and that Old Man Dexter was actually wearing a wig.
Unlike his young adult and older selves, Action Dexter is pure epic as after years of abuse from his most hated
rival, he decided he had enough and quit his job and becoming physically stronger.
Also, just like his counterparts he appears to have issues with his sister as shown when he was shocked by her sudden appearance. He also has his counterpart's tendency to complain as he stated "I wanted to be the one to save the future" after Dee Dee did so.
- Action Dexter, unlike the other Dexters, was not voiced by Christine Cavanaugh. He was voiced by Jeff Bennett instead, more widely known on the show for voicing Dexter's Father.
- He is the only one of Dexter's future selves that has not been seen in any other episodes besides Ego Trip.
- He and Action Hank have many similarities and traits.
- In a flashback scene, he is shown looking similar to Number 12, though less scrawny.
- He appears in Dexter's Laboratory: Chess Challenge as the knight for Team Dexter.
- For all intents and purposes Action Dexter is a prototype for Tartakovsky's later protagonists: Samurai Jack, of the eponymous series, and Spear from Primal. All three characters are designed around the square shapes. All three characters are heroic figures who display a loner personality with a soft side, who eventually befriend various people on their journeys. All three characters oppose an Overlord type character: Overlord Mandark, Aku and The Scorpion, respectively. And each character wields a signature weapon: a wrench, a katana, a spear, respectively.