Cher Watanabe (渡部 チェル, Watanabe Cheru, born April 1, 1968) is a Japanese composer, arranger, and keyboardist born in Tokyo. His real name is Tatsuya Watanabe (渡部 達也, Watanabe Tatsuya). He is also known as WATA-BOO.

Besides being a support musician for other bands, he also composes and arranges songs in a wide range of genres, always trying to explore new genres. After college, he was a support musician for the band JADOES. After that, he was a member of the jazz rock band SOH BAND and the progressive rock band NOA. Since 2010, he collaborated as a support member on keyboards with the fusion band Prism, which he admired since his school days; in August 2013 he joined the band as a permanent member.