Creator Genndy Tartakovsky has acknowledged taking some of his inspiration from the Frank Miller graphic novel "Ronin", including the premise of a masterless samurai warrior thrown into a dystopic future ahead of our present.
In Brazil, the name Aku was changed to Abu due to the original name's unfortunate similarity to a Portuguese swear word meaning "anus".
In seasons one through four, Aku was voiced by Mako who died on July 21, 2006. For season five, he was replaced by Greg Baldwin. Greg Baldwin also replaced Mako as the voice of Uncle Iroh on Avatar: A Lenda de Aang (2005), as Mako died during season two of that show.
"Aku" is Japanese for "evil".
When this show came back for its fifth season, it received a lot of support from fans as the show shifted from airing on the usual Cartoon Network to Adult Swim. This interesting shift meant that the writers had a more creative way to advance the plot without the restrictions placed by Cartoon Network, whose target audience is children and young adults.