The X-Men #66

In "The Mutants and the Monster," the X-Men face their most desperate mission yet when Professor X falls into a coma after battling the Z'Nox—his final mental message to them a single word: "Hulk." With Roy Thomas scripting and Sal Buscema drawing, this 1970 classic sees the team track down the Hulk, only to find Bruce Banner caught in a cycle of transformation, manipulated by Major Talbot. As the X-Men pursue him into the desert and confront the raging giant at a forgotten lab, they uncover the key to saving their leader. Cover by Marie Severin, with inks by Sam Grainger, this issue blends emotional stakes with the raw power of Marvel's earliest superhero team.