Admiral Black is a senior Starfleet flag officer, serving the Terran Empire in the Mirror Universe. He appeared in an episode of Star Trek: Enterprise entitled In a Mirror, Darkly (Part II). He was played by Gregory Itzin. Starfleet Command In the Star Trek fictional universe, Starfleet is the defense, research, diplomacy and exploration force of the United Federation of Planets. ... The Terran Empire is, in the fictional universe of Star Trek, an alternate-history counterpart of the United Federation of Planets. ... In the Star Trek television series, the Mirror Universe is an alternate reality. ... The starship Enterprise (NX-01) Star Trek: Enterprise is a science fiction television series set in the Star Trek universe. ...

When we first meet Black, he is in command of the Imperial starship ISS Avenger, which is his personal flagship at the head of an Empire assault fleet. Almost the entire strike group has been destroyed in battle with a group of rebels; Black's ship is the only one left, and is on the verge of being destroyed itself. Suddenly Jonathan Archer arrives with the captured USS Defiant (NCC-1764) and easily dispatches the rebels with his own ship's superior weaponry. ISS Avenger (NX-09) is the flagship of Admiral Black. ... Captain Jonathan Archer Captain Jonathan Archer, played by Scott Bakula, is the captain of the starship Enterprise (NX-01) in the fictional television series Star Trek: Enterprise. ... A Constitution class starship In the fictional Star Trek universe, the USS Defiant (NCC-1764) was a Federation Constitution class starship. ...

Archer expects that Admiral Black will grant him permanent command of the futuristic vessel, but Black refuses, citing a need for the Empire to take the ship and copy its technology. Black is subsequently killed by Archer.

Admiral Black may or may not have a counterpart in the 'normal' Trek universe - no such person has yet appeared onscreen.