Saint Gallus was an Admiral of the Imperial Navy who worked his way up to the rank of Lord-Admiral and eventual status as a Saint. He was the first to bring the Imperial Creed to the Legrica Sector after the initial scouting by Explorators centuries before.
Saint Gallus rose to prominence during the defence of Imperial worlds against a green tide that had been going on for years. Most of these events are lost to time now. But scholars credit him for almost single handedly breaking the Ork Waaagh. However Gallus was not content to simply defend Imperial worlds from the xenos threat. He gathered as many fleets as he could muster and mounted a counter offensive to destroy the orks at their source. It was in these years that his battles became legends. Many tales depict him exchanging mighty blows, fist to fist, and beating the orks at their own game. His campaign was remarkably successful, driving them back into the heart of the Legrica Sector. However his fleets were never able to penetrate the orks last bastion in the Rokfist Reach. The offensive slowed to a halt and a stalemate ensued for over a decade. At some point, Gallus took his flagship into the Ordallia Nebula and was never seen again.
His end may have been mysterious. But his deeds were legendary and his legacy lives on, as the entire sector was opened up for Imperial colonization.