In the mirror universe, Marcus "Mark" McHenry was a Human/Being hybrid (as he has knowledge of other universes, the ability to project his mind into other universes, his body produces bioenergy that can power a warship and an enhanced brain and intelligence level) that was "recruited" into a Thallonian secret project headed by Lord Si Cwan that was attempting to find the ultimate power source for their brand new warship; the Stinger. McHenry was compatible for the link and became a living computer system and power supply for the ship while being held in stasis in a null sphere. McHenry appeared to be in a constant medically-induced coma and Si Cwan believed himself to be in control; when, in fact, McHenry was well aware of his surroundings and was running every system on the ship and only "allowing" Cwan to use "his" ship. McHenry kept himself entertained by visiting other universes (such as the primary universe).
All this changed when M'k'n'zy of Calhoun and Soleta; teamed up with Elizabeth Shelby, Robin Lefler and Kalinda Si Cwan to commandeer the ship following the exposure of a Thallonian plot to gain power. Soleta used her own telepathic abilities to draw McHenry's mind back from his journey and convinced him to force Cwan and his crew off the ship; then M'k'n'zy took over and ordered McHenry to destroy their escape pods and launch and orbital bombardment on Danteri. Though instinctively loyal to M'k'n'zy to the point he needed his permission to cease the attack, Soleta and McHenry then forced M'k'n'zy into a vision that showed him what McHenry saw; M'k'n'zy's counterpart; Mackenzie Calhoun, a respected and liked commander of his crew (including their own counterparts, along with Shelby's, and Lefler's); this forced M'k'n'zy to order McHenry to cease the attack.
McHenry then joined the Terran Rebellion with the rest of his group; however he willingly chose to stay in the sphere to power the ship, as he "felt safe" there. (NF - Mirror Universe novel: Cutting Ties)
In 2378, in order to stop a trilithium device from destroying Bajor's sun, M'k'n'zy of Calhoun ordered McHenry to speed up the ship and ram the missile, as the Excalibur had been too far away at the time to fire. In doing so, the ship was completely destroyed, but not before McHenry had managed to place the entire crew onto the Enterprise. At first he was thought dead, but it was later revealed he had detached himself from his body and implanted himself into the Romulan Mogai-class IRW Valdore starship's Bio neural computer core. (ST - Mirror Universe novel: Rise Like Lions)