Santo was a male Twi'lek who resided on the planet of Tol Ado soon after the Battle of Yavin. A hooked scar marked his face above his left brow. Employed by a rebel group of Deathblock escapees, led by the Wookiee Warburton, Santo secretly aided the Galactic Empire. His collaboration allowed the Imperials to locate the rebel base within the sub-facility.
During 0 ABY, Luke Skywalker, disguised as an Imperial colonel, encountered Santo while he was sharing intelligence with an Imperial major and the stormtrooper TX-567. When Skywalker later sought assistance in escaping Tol Ado at the sub-facility, Santo did not recognize him; however, Skywalker recognized Santo by the moon-shaped scar above his left eye. To prove they weren't spies, Warburton tasked Skywalker and his companions, Erling Tredway and Sidney Shortfang, with ambushing Imperial resources, but the mission failed due to Santo's Imperial intel. When Warburton considered executing Tredway for his poor performance against the Imperials, Skywalker exposed Santo's Imperial alliance to the rebels. Despite Santo's denials, Warburton had him executed for his betrayal.
Troy Denning created Santo for a role-playing segment of the 1990 West End Games role-playing game supplement Jedi's Honor. The precise method by which Skywalker informs the sub-facility rebels of Santo's duplicity depends on the player's actions during the Imperial battle. If Skywalker permits Erling Tredway to bungle the ambush, Skywalker directly reveals Santo's treachery to Warburton. If he prevents Tredway's interference, he shares this information with Tormey, Warburton's lieutenant. Regardless, Warburton discovers Santo and executes him for treason.