The X-Men #25

From the Silver Age Marvel bullpen comes this 1966 installment of mutant action, with a cover by Jack Kirby and Dick Ayers that puts the X-Men on a thrilling collision course. Cyclops, Angel, and Iceman surge forward in a dynamic charge, bearing down on the massive, seated figure of El Tigre — whose imposing back dominates the foreground — while Professor X's face looms watchfully at the top of the cover. The bold cover blurb promises "The Menace of El Tigre," and Roy Thomas's story, brought to life on interior pages by Werner Roth and Dick Ayers, looks to deliver exactly that kind of pulse-quickening confrontation.