Gus was the leader of the Merry Wanderers, a group of bandits made up of deserters, murderers, and rapists located somewhere in the Riverlands.
Gus was a household guard for Joseph Baratheon at Storm's End.
Gus, along with several other members of the Merry Wanderers acted as guards for Cleos Baratheon while he was at Storm's End. However, after the fall of the Baratheons they deserted the stormlord and formed the Merry Wanderers, a bandit group.
Later, having recognized Cleos again at an inn near Ashford, Gus and his Merry Wanderers took the fleeing stag hostage, intent on bringing him to King's Landing in hopes of a reward. However, before they were able to reach King's Landing Cleos was saved by Beren Merryweather, Bonifer Tarly, Falia, and Tyro.
Gus was killed by Cleos in the aftermath of the battle.