Seago was a Manticoran citizen and an enlisted member of the Royal Manticoran Marine Corps.
In 1918 PD, Seago held the rank of Corporal and was assigned to the heavy cruiser HMS Gauntlet. While on Gauntlet, he was assigned to Midshipwoman Abigail Hearns' landing party on the planet Refuge and was killed in combat during the subsequent Battle of Tiberian. (HHA4.6: TSotS)