The Man in Black was an unnamed CIA agent who helped Professor X and his team in 2011 film X-Men: First Class.
He is portrayed by Oliver Platt, who also voiced Wiser.
History
X-Men: First Class
The Man in Black believed in mutants when nobody knew that they existed. When Professor X and Mystique came to show their powers, his mouth was open when Mystique shapeshifted and he was willing to help them. He took the team to Division X where they could be watched by the CIA.
When the Hellfire Club attacked the Covert CIA Research Base, Azazel teleported him in the air and let him fall from an altitude of several meters, killing him.