Toonami is an action animation block created by Jason DeMarco and Sean Akins that aired on weekends on Cartoon Network from 1997 to 2003, on Saturday nights from 2004 to 2008, and currently airs on [adult swim] on Saturday nights as of May 2012.
The block was and still is considered influential to the anime boom of the early 2000s, showcasing action-oriented anime such as Voltron, Robotech, Sailor Moon, Dragon Ball Z, Gundam Wing, Tenchi Muyo!, Outlaw Star, Naruto, and One Piece, as well as western-animated action shows such as He-Man and the Masters of the Universe, Batman: The Animated Series, Justice League, and Megas XLR. It was also distinctive from other animation blocks for its unique atmosphere, hip hop-flavored soundtrack, its host (formerly the Space Ghost character Moltar, now an original character named T.O.M. who has gone through six different versions as of April 2013, and his co-host Sara), and showcasing of anime music videos and video game reviews.
Big O aired on Toonami in 2001 during the afternoon at 5:30 PM and the block's Midnight Run at 12:30 AM. Edits for content were made while the show aired, such as removing religious references by digitally editing any references to God. The second season, co-produced by Cartoon Network, was not aired on Toonami and instead premiered on [adult swim]. In anticipation of the second season's premiere, the first season was re-aired on [adult swim] completely uncut and unedited. In July 2013, shortly after Toonami was revived as a Saturday night block on [adult swim], the second season of Big O made its debut on Toonami at 3:30 AM, coinciding with the premiere of Sword Art Online, and was given a second run in October 2014.
- For some time, Toonami was only able to air the second season, due to Cartoon Network co-producing it and giving them perpetual airing rights to it, while the first season remained in licensing limbo after Bandai Entertainment halted DVD production. Even after both seasons were licensed by Sentai Filmworks, Toonami has yet to announce plans on airing the first season.
- The quote "Good guys still wear black" from the 2001 Toonami promo is a callback to Toonami's promo for Batman: The Animated Series, and a reference to that show's influence on Big O.
- Steve Blum, the voice actor for Roger Smith in Big O, began voicing T.O.M. during the character's second iteration (replacing Sonny Strait), and continues to voice the character.