Boss Gallo was a Gungan warlord who lived on the planet Naboo millennia before the Imperial Era. At the time, the Gungan tribes were constantly at war with each other, until Gallo dominated the Gungan cities and united them under a single banner using diplomatic and military tactics.
Gallo rallied a massive army to destroy the ancient fortress city Spearhead, the home of the rogue Boss Rogoe and the remaining holdouts against Gallo's united Gungans. Gallo then had a new Gungan capital called Otoh Gunga built on top of Spearhead, with the original foundations laid by Gallo becoming known as the Ancient Quarter.
Behind the scenes
Gallo was first mentioned in the new Star Wars canon in Nexus of Power, a 2016 sourcebook published by Fantasy Flight Games for the Star Wars: Force and Destiny roleplaying game. In the Star Wars Legends continuity, Gallo was first mentioned in Star Wars: Galactic Battlegrounds: Prima's Official Strategy Guide, released on November 7, 2001, before appearing in the LucasArts video game Star Wars: Galactic Battlegrounds, released on November 11 the same year.