In the mirror universe, the ISS Avenger (NX-09) was a NX-class battle cruiser of the Terran Empire. The ship's motto, seen on its mission patch, was Audentes Fortuna Imperii—"the bold are the fortune of the Empire".
In 2155 the Avenger was the flagship of Admiral Gregory Black and part of an assault fleet that was almost totally destroyed in a battle with rebels. Fortunately, the USS Defiant, commanded by Jonathan Archer arrived and drove the rebels off with its advanced weaponry. However, Archer planned to become Emperor and killed Black taking command of Avenger. The aliens on board led by Soval attacked the Defiant while it was sabotaged by Phlox. The Constitution-class's crew were able to restore its systems and Avenger was destroyed. (ENT episode: "In a Mirror, Darkly")