This is going to be a quick one.
Negasonic Teenage Warhead is a Genoshan mutant who first appeared in New X-Men #115 (June 2001). She was a telepath who also had some precognition powers:
Surprisingly, she appeared in Deadpool (2016), although with a different look, backstory, and power set. Her role in the film was originally meant for Cannonball, but they couldn't use him, so they picked Negasonic based solely on her name. Frankly, her name makes more sense for someone with explosive powers like she has in the film:
She has since started appearing in Deadpool and the Mercs for Money (July 2016, et al.) with a look clearly inspired by the movie. Her association with Deadpool at all derives from the movie, in fact.