X-Men: Days of Future Past is a classic X-Men storyline written by Chris Claremont and illustrated by John Byrne. In this dystopian future tale, the X-Men must prevent a catastrophic event that leads to the persecution of mutants. The story features a time-travel plotline and explores themes of prejudice, identity, and sacrifice. With its iconic characters and gripping narrative, Days of Future Past is considered one of the greatest X-Men stories ever told.