The Beatles Revolver. Actually, their reinvention started with the 45 RPM single that preceded that album: "Paperback Writer"/"Rain". A group changing their sound that much (from the Rubber Soul album) was at that time considered very risky, the possibility of losing one's fan base a very real risk.
Perhaps the most fearless, brave artist of them all is Bob Dylan. Going electric alienated a lot of his older, Folk purist fans. He didn't care. Going "Christian" was another brave move, alienating even John Lennon, whose songwriting was hugely impacted by Dylan. Finding religion was a step too far for him (from Lennon's "Imagine" song: ....."imagine no religion".).
Perhaps the most fearless, brave artist of them all is Bob Dylan. Going electric alienated a lot of his older, Folk purist fans. He didn't care. Going "Christian" was another brave move, alienating even John Lennon, whose songwriting was hugely impacted by Dylan. Finding religion was a step too far for him (from Lennon's "Imagine" song: ....."imagine no religion".).