The Yamaha GX-1 is one of rarest and most expensive synthesizers ever built. It Debuted in 1975 at a cost of $60,000 (close to $320,000 in 2016 money), and served as a test bed for future synthesizer technology (mostly the Yamaha CS80). Fewer than 100 were made, and only about 13 are estimate to exist outside of Japan.
Mostly notable users include Keith Emerson who used it on Works Volume 1 & 2, Love Beach, Emerson Lake & Powell, as well as using it on the Works Tours (the famous Fanfare for the Common Man synth) .He eventually ended up owning 2 GX-1s
John Paul Jones used it on the Zeppelin album In Through The Out Door an the 1979 shows. He later sold his to Keith Emerson.
Richard Wright owned one briefly, but never recored any music on it.
Stevie Wonder owned one and used it on Songs In The Key Of Life
Benny Andersson of ABBA used it on several records an live shows.