CT-27-5555, also known as ARC-5555 and later re-designated as CT-5555, was a clone trooper who served in the Grand Army of the Republic during the Clone Wars. Because of his clone designation, he was given the nickname "Fives." Around 22 BBY, right about the time that the clone war had begun, Fives was assigned to Domino Squad, a unit of clone cadets that trained within the planet Kamino's Tipoca City military complex, under the command of the Siniteen Sergeant Bric. Fives and his squad were required to pass a test in order to become battle-ready clone troopers. After the completion of their training, Fives, along with a number of other rookie clone troopers, was assigned to Rishi Station, a listening post located on the moon of Rishi. Fives was present when the Confederate General Grievous invaded the moon to take control of the Republic listening post. With the arrival of Clone Commander Cody and Clone Captain Rex, the two clone officers helped Fives and the surviving rookie troops retake the outpost.


Fives and trooper Echo, the only rookie survivors of the battle, were rewarded with medals for their service on the Rishi moon and were inducted into the 501st Legion. They later helped defend Kamino after Grievous, along with Dark Acolyte Asajj Ventress, invaded the planet and attacked Tipoca City. Following the Confederate attack on Kamino, Fives and Echo were promoted to ARC troopers for their continuous efforts. As the war continued, both Fives and Echo joined Jedi Generals Obi-Wan Kenobi and Anakin Skywalker in the rescue of Jedi Master Even Piell from the Confederate prison known as the Citadel. After they rescued Piell and his officers, the facility's warden, Osi Sobeck, released battle droid forces on Fives and the Republic group. While Echo and Piell perished during the battle, Fives and the surviving members of his team were rescued by Jedi Master Plo Koon