IMPERIALS WHO FOUGHT FOR THE REPUBLIC
When the Clone Wars began, Wilhuff Tarkin enlisted as a captain in the newly-formed and militarized Republic Navy, departing his role as governor of Eriadu and rejecting an overture from Dooku to join the Separatist cause. He’d previously worked with both the Jedi and then-Senator Palpatine and eventually rose to the rank of admiral. When the Republic transitioned into the Galactic Empire, Tarkin was formally made a Moff by Emperor Palpatine.
After his ascension to the rank of Jedi Knight, Anakin Skywalker became a general in the Grand Army of the Republic during the Clone Wars, commanding the 501st Legion of clone troopers. After pledging himself to Sidious and taking the name Darth Vader, he killed the entire Separatist leadership, effectively ending the Clone Wars. As the Emperor’s enforcer, he retained command of the 501st Legion, now stormtroopers, which soon became known as “Vader’s Fist”.
Prior to the Clone Wars, Wullf Yularen served as a captain in the Senate Bureau of Intelligence, assigned by Chancellor Palpatine to an anti-corruption unit. When the Clone Wars began, Yularen joined the Republic Navy as an admiral and was assigned to Jedi general Anakin Skywalker. After the war, Yularen resigned his commission to join the Imperial Security Bureau with the rank of colonel, where he worked to root out sedition within the Imperial Senate.
I figured it out.