Uncanny X-Men #60

60

"In the Shadow of... Sauron!"

September 1969

The X-Men take Alex to Dr. Karl Lykos, who is revealed to be Sauron

marvel.com

reprinted in

* 40 Years of X-Men 2005, in collection (2005*)
* X-Men: Visionaries: Neal Adams TPB 2000, in collection (2000*)