Guess I was fooled back in 2011 - I thought Courtney Love was on the back cover of the Grateful Dead's Aoxomoxoa. Apparently not.
Just as surprising though is somebody who does show up in that photo, Vince Guaraldi, who brought us the immortal music of "A Charlie Brown Christmas" most notably the incredibly catchy "Linus and Lucy."
I was amazed to read that Guaraldi allegedly sat in with the Grateful Dead in the early 1970s. Although if that's so, it's odd that there's apparently no certain recording of him playing with them, considering how thoroughly Grateful Dead shows were documented through their career. This guy seems to think he sat in on New Year's Eve 1968.