When the X-Men creative team was about to change in 1977, Dave Cockrum drew this cover for The Comic Reader #145.
John Byrne introduces himself to the X-Men, who have no idea who he is or why Cockrum is missing.
I can't remember exactly, but I believe this cover appeared a few months before John Byrne's first issue of the X-Men, #108, cover dated December. I do remember feeling the loss of Cockrum on the title, but feeling like Byrne could pull it off, since he had done so well on Starlord (see Claremont, Byrne & Austin's Classic Take on Star-Lord) and Iron Fist.
It was a great way for Dave Cockrum to hand over the reins of the X-Men, a title he visually re-designed for a new era. Nuff Said!