The X-Men are a group of Superheroes in the Marvel Universe.
In Marvel's Midnight Suns[]
Magik is a member of the X-Men who is recruited to the Midnight Suns in the Prequel Short A New Sun Must Rise. She is part of the team at the start of the game.
The Midnight Suns meet 
Wolverine, a notable X-Men member, during the mission The Best There Is. He joins up with the Suns following the events of The Changing Face of Evil.
Storm, who is part of the Blood Storm DLC, is another member of the X-Men. At the start of the mission Hard Knock Life, which takes place some time after the events of The Best There Is, she contacts Magik and Wolverine for assistance. After that mission, she is introduced to the Midnight Suns and becomes available as a playable character. She formally commits to staying on with the Suns at the end of Where the Blood Flows Like Wine.