Isao Sasaki (ささき いさお(佐々木 功), Sasaki Isao, born May 16, 1942) is a Japanese actor, voice actor, and singer.
He has had voice roles in anime such as Legend of the Galactic Heroes, Space Battleship Yamato, and Gatchaman. He has also performed the opening themes for anime such as Yamato, Star of the Giants, Getter Robo, Casshern, Grendizer, Gaiking and tokusatsu series such as Himitsu Sentai Gorenger, J.A.K.Q. Dengekitai, Choujinki Metalder, and most recently Tokusou Sentai Dekaranger. He has also had an acting role in the tokusatsu film Kamen Rider ZO, OOO, Den-O, All Riders: Let's Go Kamen Riders and in the series Kyojuu Tokusou Juspion. He is the official dub voice of Sylvester Stallone, and Christopher Reeve's Clark Kent and Superman in the film series, until he was replaced by Hiroki Tōchi for Superman Returns.