Callan Grayne was a Human male who served in the Republic Army during the Great Galactic War with the Sith Empire, and later became a general in Republic Strategic High Command during the subsequent Cold War. As the Galactic War broke out with the Empire at the end of the Cold War, Grayne was sent to the icy planet of Hoth to take charge of the Republic offensive there. While coordinating the Republic Military on the planet, Grayne enlisted the aid of the Jedi Knight known as the Hero of Tython, and later assigned Sergeant Fideltin Rusk to the Jedi on the order of fellow High Command member Durant.
A Human male, Callan Grayne joined the Republic Army sometime after 3665 BBY and was placed in a squad that included the Chagrian Fideltin Rusk. The two served together for some time during the Great Galactic War with the Sith Empire, fighting in engagements such as the Geonosis campaign, in which they worked alongside a Human named Durant. During Grayne's time with the squad, he was injured in battle and lost his entire left leg, though doctors fitted him with a convincingly lifelike prosthetic.
The war ended in 3653 BBY with the signing of the Treaty of Coruscant, and during the subsequent Cold War Grayne became a general in Republic Strategic High Command, the highest level of command within the Republic Military. Around 3642 BBY, Grayne was dispatched to take control of the Republic military forces on the planet Hoth, which was becoming the site of a three-way battle between the Republic, the Empire, and the White Maw pirates. All three factions were fighting for control of the ruined starships and prototype technology that had been scattered across the planet's surface since the Battle of Hoth over a decade prior in 3665 BBY. Arriving in orbit, Grayne was alerted to the presence of several Imperial weapons platforms on the edge of Crescent Canyon, which was located only a short distance away from the Republic's Aurek Base on the west edge of the Icetromper Wastes. Learning that two Jedi Knights, Leeha Narezz and the Jedi known as the Hero of Tython, had commandeered the 301st Infantry for a covert mission, Grayne contacted the Hero. As General Var Suthra had spoken highly of the Knight's military prowess, Grayne requested that the Jedi help the Military in return by destroying the emplacements and eliminating the threat they posed.
A short time later, Grayne learned that Rusk, now a sergeant in the 301st, was about to attack a White Maw base in the Glacial Fissure region as part of the Jedi mission, and he ordered Rusk's squad to destroy several nearby munition dumps and thereby weaken the White Maw. After the Jedi completed the mission, Grayne spoke with fellow High Command General Durant, and the two decided to rotate the 301st Infantry back to the Republic capital of Coruscant and send the 88th Armor in its place. However, Durant also decided to indefinitely assign Rusk to the Hero in order to aid the young Knight, and Grayne requested a meeting with Rusk's squad and the Jedi at Aurek Base. The general relayed Durant's orders to Rusk after a brief reminiscence of their time serving together, then returned to overseeing the battle against the Empire on Hoth.
As a result of his service during the Great Galactic War, Grayne sported a prosthetic left leg. On Hoth he wore gray, white, and maroon combat attire suited to the cold weather.
Callan Grayne appeared in Star Wars: The Old Republic, a video game released by BioWare and LucasArts in 2011, in which he is a recurring character in the Hoth storyline for the Jedi Knight class. Grayne contacts the player in the mission "Suicide Squads" and requests aid for destroying nearby weapons emplacements, and Sergeant Rusk contacts the player in the mission "Position of Power" with an additional objective of targeting munitions dumps. Grayne finally appears in person at the end of "The Price of Victory," in which he assigns Rusk to the Knight and thereby grants the player his or her fourth companion character.