In the mirror universe, Staal was a male Vulcan in the 22nd century.

Early in life, Staal had undergone cosmetic surgery to appear human (a process known as "species reassignment"), and had taken the human alias "Willingham" in order to better integrate into the Imperial Starfleet. As an ensign aboard the ISS Enterprise (NX-01), he managed to pass undetected until 2153, when his true nature was discovered by Commander T'Pol.

T'Pol opted to keep Staal's secret, believing he could be of use as an ally. This proved true in 2155, when T'Pol was arrested for attempted mutiny against Captain Jonathan Archer, and Staal helped affect her release from the brig. Staal and T'Pol then escaped the USS Defiant aboard the shuttle McCool, fleeing together to planet Vulcan.

On Vulcan, Staal and T'Pol connected with a cell of rebels against the Terran Empire led by T'Pau. However, when T'Pau began to doubt T'Pol's loyalty to their cause, she charged Staal with killing T'Pol. T'Pol was able to repel his assault, and instead killed Staal herself.

In a mind-meld just prior to death, Staal also admitted to having killed T'Pol's mother, T'Les, at T'Pau's command. (ENT - Mirror Universe novel: Age of the Empress)

It is unknown if Staal has a counterpart in the primary universe.
ISS Enterprise (NX-01) personnel
Terran Empire
Imperial Starfleet
Jonathan ArcherMaximilian ForrestKelbyNewbillPhloxHoshi SatoStaal (Willingham)T'PolTerevCharles Tucker IIIunnamed ISS Enterprise personnel TerranEmpire
Terran Empire
HaffleyMatthew KellyMaddenMcCainTravis MayweatherMalcolm Reed