From Zappa Wiki Jawaka
Jack Bruce (Born John Symon Asher Bruce, May 1943, Bishopbriggs, Lanarkshire, Scotland.
Jack Bruce's friendship with FZ drummer Jim Gordon brought about a meeting between Bruce and Zappa, and a jam-session followed. This session took place in September, 1972, at Electric Lady Studios, Greenwich Village, NYC, with Bruce on bass, FZ on guitar, Gordon on drums and Tony Duran on rhythm guitar. This resulted in Bruce providing bass on the title track of Apostrophe (').
Bruce had achieved a rock-cult status with John Mayall & the Bluesbreakers and went on to form the 'supergroup' Cream with Eric Clapton and Ginger Baker. At the time of the above session he had just departed the band "West, Bruce and Laing". (More info at Jack Bruce bio).