The show's title character is the superhero alter ego of geeky sixteen-year-old Dexter Douglas (voiced by David Kaufman) who attends Harry Connick High School. His name is a parody of various superheroes with the first and last names using the same first letter or sound (e.g. Clark Kent, Peter Parker, etc). Gaining his abilities from a computer bug (becoming absorbed into his computer and instantly gaining all the information on the Internet), Freakazoid (voiced by Paul Rugg) has enhanced strength and endurance, extraordinary speed, agility, and negligible amounts of sanity. These changes make him a powerful and fearsome force for upholding freedom and righteousness, unless he gets distracted by something like a bear riding a motorcycle. He has a base called the Freakalair, a parody of the Batcave, built by his mute butler, Ingmar. The Freakalair contains a "Hall of Nifty Things to Know" and even a mad scientist lab. His greatest weakness, as he once explained to a villain, is that he can be imprisoned in a cage with graphite bars charged with negative ions. He also expresses a great aversion to "poo gas."
Peripheral powers come and go: Freakazoid once developed telekinesis triggered by anger that was never mentioned again after the episode, and once crossed the globe to yell at a Tibetan monk for raking too loud. He also has the ability to assume the form of electricity and cover long distances instantaneously, although he just as often simply sticks his arms forward and runs while making swooshing sounds with his mouth, pretending to fly.
Dexter can change into and out of Freakazoid at will with the words "Freak out!" and "Freak in!" When not in Freakazoid mode, Dexter looks and acts completely normal, and his family is unaware that anything has happened to him. Freakazoid spends this time in an area of Dexter's brain called the Freakazone, where he reflects, has profound thoughts, and watches reruns of The Rat Patrol.
The "secret key sequence" that must be typed for the computer bug to become active begins with: "@[=g3,8d]&fbb=-q]/hk%fg" (the quotes are included) as seen when Roddy MacStew types the combination in "The Chip (Act IV)". The bug manifests when the user presses Delete after entering the string. The bug was first manifested when Dexter's cat crawled onto the keyboard.
While the show's setting is set around Washington D.C., the locale often varies with the show's humor, taking Freakazoid to locations around the world as needed.