Mandalore the Advancer was a Mandalore in command of all Mandalorians and founder of the clan Mandalorian Legion.
Apparently, he was raised by Canderous Ordo's late descendents after his mother died giving birth to him and his father was sent to prison for murder. He underwent demanding training by the age of ten, and knew fully well how to use a rifle by the age of 13, and even killed someone who used to bully him when he was little by the age of 14. He continued training and left for military school at the age of 16. After one year in military school, his commanding officer said he was the best recruit he ever had, and thus making a Rodian recruit jealous. It resulted in laserfire exchange between the two, and Mandalore killed the Rodian and was expelled for murdering a fellow recruit and wa sto serve a custodial sentence, but made a run for it after killing the police force guards on Mandalore. He returned to Ordo's descendants and thanked them for bringing him up and training him. He then said he would promise to be as much like Canderous as he could and joined the Mandalorians.
He then became Mandalore after seventeen good years of service for the Mandalorians and took the title Mandalore The Advancer, telling all Mandalorians he would advance them and make them a powerful force, and he did just that by fighting the Empire and becoming allies with the New Republic.