Why does a woman voice Goku?
The casting was the author's call. When Toei prepared the Dragon Ball anime in 1986, Akira Toriyama chose Masako Nozawa for Goku after hearing the audition performances, and later said that once he had heard her, he heard Nozawa's voice in his head while writing the manga. Nozawa was no newcomer handed a lucky break: she had been a leading voice since playing Kitaro in GeGeGe no Kitaro in 1968 and Tetsuro in Galaxy Express 999, and she had been delayed, not helped, by a Fuji TV convention that a voice actor should not carry two lead roles at once, without which, she has noted, she might never have been free to audition.
The reason the question exists is the decision that followed. Japanese animation commonly keeps a child character's performer into adulthood where a male recast would break continuity, and Nozawa's Goku simply never stopped: she voiced the child of 1986, the adult of Z, the father, and the grandfather, and the production built the family around her voice. She is also Gohan and Goten, and Bardock, and later the villain Goku Black, which means entire conversations and fights in the series are one performer arguing with herself. Colleagues describe the method plainly: when Goku, Gohan, and Goten share a scene, she records all three in the same take, switching on the spot, a feat Toshio Furukawa has said no one else can do, and one she explains by refusing to switch at all: the characters, she says, live inside her.
The records followed. In 2017 Guinness World Records certified Nozawa in two categories, the voice actor who voiced the same character in a video game for the longest period, and the longest video game voice acting career, measured at 23 years and 218 days of playing Goku in games, from Super Butoden in 1993 to Xenoverse 2. Toriyama sent a message to the ceremony saying he felt a bit proud to have a small connection to the records. In December 2023 she became the first voice actor ever to receive the Kikuchi Kan Prize in its 71 year history. Goku sounds like Nozawa because, for forty years and counting, Goku is Nozawa.