Born into a Quillar farming family on the Lyran Commonwealth border world of Alexandria, the death of Galen's parents during a House Kurita attack in 3039 drove the young man to enlist in the newly created Armed Forces of the Federated Commonwealth to avenge them. His natural aptitude for piloting BattleMechs secured him a MechWarrior training position at the War College of Tamar, graduating in 3042. 
Assigned to the 12th Donegal Guards stationed on Ryde, Galen was soon promoted to Company command for his actions at the controls of his Crusader against raids by the DCMS. In 3050 when the unseasoned heir to the Federated Commonwealth Victor Steiner-Davion was assigned to command an entire Battalion in the Twelfth directly after graduating from the Nagelring, Galen volunteered to "nursemaid" him through his first assignment. 
At first Victor resisted the approaches of his ill-defined aide, but came to recognize that Galen was attempting to be the exact opposite of the spine-less "Yes-Man" he had come to expect. When Clan Jade Falcon virtually overran their unit on Trellwan during the opening shots of the Clan Invasion, Galen's role was put to the ultimate test when he was forced to knock the prince out to ensure Victor could be safely evacuated off-world.
Continuing to serve as Victor's Adjutant upon the Prince's transfer to command of the 10th Lyran Guards, Galen saw action on Twycross, Alyina and Teniente as a genuine friendship developed between both men. Upon Hanse Davion's death shortly after the Battle of Tukayyid and Victor's elevation to rule of House Davion, Galen was appointed to the position of Prince's Champion as he began a relationship with Victor's younger sister Katherine Steiner-Davion, the pair becoming engaged in early 3056.
However in April 3056 during a visit to Solaris VII, he was believed killed in a bomb assassination ordered by Ryan Steiner. In actuality, he had been spared when MIIO agents had linked his fiancee to the bomb assassination of Melissa Steiner-Davion, and in turn discovered the warning passed on to her by a mole she had placed in Ryan Steiner's staff.
Several months later, having underground plastic surgery and wearing a thick beard to help differentiate himself from his previously clean-shaved look, Galen Cox emerged as Jerrard Cranston, a personal aide to Prince Victor.
With his cover identity background intended to be roughly similar to his true one to avoid question while explaining his background and military experience, Cranston supposedly hailed from Callison in the Isle of Skye, being first posted to the 11th Lyran Guards before being transferred to the 1st Lyran Guards RCT, seeing action against the Clans on Maestu in 3051.  Reportedly retiring from military service shortly after the Battle of Tukayyid, Cranston official records abruptly ceased until he mysteriously appeared at Victor's side.
While Cranston publicly served as an minor aide to the Archon-Prince to cloak his responsibilities, in actual fact Galen served as primary Intelligence adviser for Victor. Upon Victor's return from Clan-space and following Katherine's coup against Regent Yvonne Steiner-Davion in 3061, Galen accompanied him into exile, shattering his humble facade when he was formally appointed Director of Intelligence for the Star League Defense Force later that same year.
Even while serving in this position, Galen continued to funnel info and maintain connections in both the Lyran Alliance and Davion Federated Commonwealth to assist Victor in the approaching conflict. After the Federated Commonwealth Civil War official started, Galen once again returned to the position of formal personal aide for his friend. At the conclusion of the Civil War with Katherine deposed, Galen abandoned the Cranston persona. 
Galen Cox Once More
Galen Cox led ComStar's 2nd Army during Operation SCOUR, the allied coalition campaign to liberate the worlds of the Word of Blake Protectorate. With the 2nd Army operating as a part of Group II of the Federated Suns front of SCOUR, Galen Cox would lead the assault on Fletcher alongside Connor Sortek and the 1st Davion Guards in what would prove to be a short campaign; the two coalition units easily crushed the defending Blakist forces, something the Federated Suns media considered a foregone conclusion at the time due to the units and personalities involved.
It was confirmed by General Belle Lee that during the campaign against Terra itself, Cox would be leading the ground assault near Texas in North America, while his former Group II compatriot Connor Sortek led the campaign against Unity City on the same continent.
- Masters and Minions: The StarCorps Dossiers, pp. 208-209
- Shattered Sphere, p. 26, 35
- Jihad Hot Spots: Terra, p. 39-40, "Ingress, Fletcher Fall"
- Jihad Hot Spots: Terra, p. 93, "Force Breakdown"
- Storms of Fate, p.??