Blanch Sproull was a mechanic of the human species who served the Alliance to Restore the Republic. Their military rank was that of a private. Sproull, convinced of the Rebellion's righteousness, departed their home on a mining planet to enlist. They were stationed on the Spirit of Jedha transport during an evacuation of the rebel outpost located on Lowik, alongside other transports. Although Sproull inspected the hyperdrive converter, it failed during hyperspace travel, resulting in an attack on the Spirit of Jedha by pirates belonging to the Ohnaka Gang. Beilert Valance, a bounty hunter dispatched by Lieutenant Kondra to save the rebels, was unable to protect the transport. Commander Hill Purpura, questioning Valance's loyalty, ordered him imprisoned on the vessel. While Purpura attempted to negotiate a surrender with the pirates, Sproull was assigned to guard Valance, but instead, freed him, which allowed Valance to escape in a partially operational X-wing starfighter.