The series involves a boy genius named Dexter, who has a secret laboratory filled with highly advanced equipment, hidden behind a bookshelf in his bedroom. Access to this never-ending laboratory is achieved by saying various passwords or by activating hidden switches on the bookcase. Dexter is almost always in conflict with his obnoxious older sister, Dee Dee, who delights in playing in her brother's lab, often destroying his inventions and creations.

Samurai Jack  is the son of the lord who ruled the area where Aku originally appeared on Earth, and is banished to the future by Aku during their first battle, where he is left in every episode to search for a way home.

As a boy, Jack traveled around the world to prepare both physically and mentally for his confrontation with Aku He studied under various scholars, such as Greek thinkers, and attempted to master each art of combat from the cultures he met, training with Vikings sailors, Robin Hood,  Shaolin monks, Greek Olympic contestants, and several others. Jack's magic sword was forged by the gods Odin, Ra, and Rama through 3 mortal avatars. The sword was forged of the pure spirit of good that humans possess, extracted from Jack's father.