Toshiko "Tosh" Sato(佐藤敏子Sato Toshiko, English pronunciation:/ˈtɒʃɨkoʊ ˈsɑːtoʊ/) is a fictional character from the television series Doctor Who and its spin-off Torchwood, played by Naoko Mori. She is a regular in the latter programme for the first two series, but actually first appeared in the Doctor Who episode "Aliens of London". In Torchwood, Sato is the Cardiff branch's "technical expert", described as "quiet but highly intelligent", and a "computer genius".