The following section contains information from StarCraft: Insurrection.
Andraxxus was a protoss executor who commanded the Koprulu Expeditionary Force's 7th Fleet. He was in charge of purging the infestation of Brontes IV, but was eventually destroyed by zerg forces there..
At the age of 314, Andraxxus was given command of the 7th Fleet by Executor Tassadar, tasked with destruction any planets in the Brontes System infested by the zerg. Andraxxus was willing to obey, though grappled with the morality with the situation given that terran lives would be lost also. This was in contrast to his advisor, Judicator Syndrea, who saw the terrans as savages. Regardless, Andraxxus led his fleet to Brontes IV, the source of the infestation, securing the space above it. Protoss ground forces were then dispatched to the planet's surface. Andraxxus left to purify the surrounding planets of zerg infestation, leaving Syndrea in charge of securing Brontes IV with the aid of his trusted advisors, Edullon, Demioch and Aedus/Xerxes.
Despite the protoss' initial victories (and those of their allies in the New Dresdin Outlaws), the situation began to deteriorate. The vanguard on Brontes IV fell into infighting, leading to the death of Aedus/Xerxes and the capture of Syndrea by the Zerg Swarm. Andraxxus's fleet was defeated by Nargil and the Fenris Brood, and was forced to retreat to their stronghold on Brontes IV while the zerg secured the space around the planet. Anger began to take hold of Andraxxus, prompting him to rashness. He attacked the both Carpenter's Brood and the Zerg Swarm simultaneously. However, Black Morgan, a New Dresdin Outlaws member, had been infected by a parasite, leading the zerg to Andraxxus' position. The zerg attacked en masse, killing Andraxxus along with the entirety of 7th Fleet.