The mutant Domino is an ally of the X-Men most commonly associated with their paramilitary black-ops team, X-Force. Although she debuted in the early '90s, Domino typically has not enjoyed the massive popularity of other characters affiliated with the X-Men such as Wolverine and Deadpool. However, her popularity has seen a massive spike as of late with her inclusion and co-starring role in the second Deadpool movie.
Domino made her fist comic book appearance in the same issue as Deadpool: New Mutants #98. Domino showed up as Deadpool was attacking the team and put him down by throwing a few blades in his back. Cable, the leader of the New Mutants at the time, was very happy to see her and Domino explained her presence by simply saying, "You called, I came."
Domino stayed on with the team, who immediately saw she had an effect on Cable. Normally a grizzled old soldier who acted like he was constantly on a mission, Domino's presence on the team led to Cable cracking the first smile his teammates had seen. She also helped him become more of a father figure and teacher to the team, whereas before he acted like a Drill Sergeant whipping soldiers into fighting shape.
Domino immediately took the reigns of co-leadership, her previous relationship with Cable automatically making her a trustworthy ally as far as he was concerned. Although she remained an enigma to the other members of the team, Cable made her his right hand and intimacies that were a part of their shared past were brought to the present. Domino became a confidant for the old fighter as well, helping him train the "soldiers for his war," as well as recruit others to his cause.
However, all was not as it seemed. Over a year after being introduced and accepted into the ranks of the New Mutants (who by this time had been transformed into the paramilitary group X-Force), it was revealed that Domino was not who she claimed to be. In X-Force #11, while the majority of the team in is the Morlock tunnels, Deadpool sneaks into X-Force's headquarters and after knocking out Shatterstar, attacks Domino.
During the course of their fight, Deadpool reminds her she isn't Domino at all, but rather his old girlfriend Vanessa, aka the shapeshifter Copycat. As he pummels her, he tells her their mutual employer, X-Force's enemy Tolliver, is upset she hasn't made contact recently. The mercenary asks her to tell him she remembers her infiltration of X-Force is just a job and that she isn't falling for Cable. When she is unable to do so, their fight resumes.
After Deadpool wins the fight and Copycat is at his mercy, he slams a knife down next to her and reminds her that she still works for Tolliver. Before he leaves, he tells her his attack was a friendly reminder and that he won't be as nice if he has to tell her again.
At the conclusion of the issue, the real Domino is seen for the first time as the tortured prisoner of Mr. Tolliver.
In terms of first appearances, Domino's is certainly a bit bizarre. For over a year, the Domino fans were seeing every month in the pages of New Mutants and X-Force was not the real version of the character. Still, Domino has managed to garnish her fair share of fans despite the initial deception, a feat that may have as much to do with her trademark good luck as her appearance in the Deadpool sequel.