William Riker

William T. Riker was a human male in several permutations of the Mirror Universe. He was the mirror counterpart of William Riker.

In several Mirror Universe offshoots Riker was an officer of the Terran Empire's Imperial Starfleet.

Dark Mirror
In a version of the Mirror Universe where Spock was killed before he could implement his reforms, the Terran Empire never fell. In the 2360s the Empire fielded the starship ISS Enterprise ICC-1701-D, and Riker was tapped to serve as first officer under the command of Jean-Luc Picard.

Riker spent most of his time plotting to have Picard killed and take command of the Enterprise for himself. Working with security chief Deanna Troi, the pair would often subject various crew mmembers to holodeck simulations to gauge their loyalty.

When the prime universe Jean-Luc Picard infiltrated the Enterprise Riker - not knowing the transposition had occured - allowed Wesley Crusher attempt to assassinate Picard. Crusher failed in his attempt, but Picard strongly suspected Riker had allowed or even encouraged Crusher to make the attempt.

Mirror Broken
In the Mirror Broken comics, the Terran Empire had been reduced to a rump state contained in the Sol system. In the 2360s Riker was tapped by Picard to be first officer on the new Galaxy-class ISS Enterprise (NCC-1701-D).