The Big O is an anime TV series created and produced by Sunrise. It was directed by Kazuyoshi Katayama (Appleseed, Argento Soma), with character and mecha designs by Keiichi Sato (Mazinkaiser, The SoulTaker), and script by Chiaki J. Konaka (Armitage III, Serial Experiments Lain).

Forty years prior to the events of the series, a mysterious occurrence caused the residents of Paradigm City to lose their memories. The series follows Roger Smith, Paradigm City's top Negotiator. He provides this much needed service with the help of an android named R. Dorothy Wayneright and his butler Norman Burg. When the need arises, Roger calls upon Big O, a giant relic from the city's history that may hold the key to its future.

The Big O is designed as a tribute to Japanese and Western shows from the 1960s and 1970s. The series is done in the style of film noir and combines the feel of a detective show with the mecha genre of anime. The setpieces are reminiscent of Toho monster movies and the score is an eclectic mix of styles and musical homages.

The series premiered October 13, 1999 on WOWOW satellite television. It finished its run on January 19, 2000. The English language version premiered on the American Cartoon Network on April 2, 2001. Originally a thirteen-episode series, positive fan response internationally resulted in a second season co-produced by Cartoon Network, Sunrise, and Bandai Visual. Season two premiered on Japan's SUN-TV on January 2003, with the American premiere taking place seven months later.

Roger Smith acts as a negotiator in a city where everyone has lost their memories and keep it that way. When he isn't helping hostage situations, he's saving the day in a giant robot known as Big O. Although Roger has no idea why the "megadeus" (Big O) responds to his commands or why his butler seems to be a master at fixing the high tech machine, he starts to question the forgotten past after the events started by an unsual case involving an android called R Dorothy. While he and Dorothy begin a Henry Higgins/Eliza Dolittle style of friendship, villains and mysterious characters enter with clues leading up to something that may bring out an emotion Roger has tried to fight all of his known life - fear. Written by Max Vaughn