The story of Big O takes place 40 years after an incident called "The Event" occured which destroyed the city of Paradign and erased the memories of the citizens. Even though the lives of the citizens eventually return back to normal and the citizens remember the use of technology like electricity and automobiles, they are still plagued with the problem of not knowing what had exactly happened to them over 40 years.
The main characters name is Roger Smith who is known as the Negotiator. It is his job to protect the people while he deals his own mysterious past. His allies are Dorothy an andriod, his butler Norman, and a giant Robot called the Big O.
Big O is a combines ideas from shows like Batman, Giant Robo, Outlaw Star, and Gundam Wing. The Big O was written by Chiaki Konaka, who also wrote scripts for Bubble Gum Crisis, Magic Users Club, and Serial Experiments Lain.