Since it formed in 1968 at the dawn of the U.K.’s progressive-rock era and quickly became the genre’s defining champion, Yes has witnessed innumerable lineup changes, not to mention splinter bands, sub-groups and solo projects. But few fans would argue that the definitive quintet coalesced on album and onstage with vocalist Jon Anderson, bassist Chris Squire, guitarist Steve Howe, drummer Alan White and the flamboyant, cape-wearing keyboardist Rick Wakeman.