Prior to taking up the title of Mandalore, this Mandalorian warrior was a soldier during the Sith War. Their leader, Mandalore the Indomitable, was killed in the hostile jungles of Dxun. This Mandalorian warrior who would be called "the Ultimate" found the helmet of Mandalore, claiming it as his own and proclaiming himself the leader of the Mandalorians, Mandalore the Ultimate.
Twenty years later, Mandalore the Ultimate led the Mandalorians on a great campaign, conquering countless planets across the galaxy. The war was brutal, and the Mandalorians emerged victorious at nearly every turn. The Jedi refused to intervene and the Republic was nearly powerless to stop the Mandalorian advance.
One day, however, one Jedi rose to the fight. His name was Revan, and he was a very charismatic Jedi, bringing many Jedi Knights to his cause in direct defiance of the Jedi Council. The media would call him the Revanchist; those that followed him were called Jedi Crusaders, or the Revanchists. Under Revan's strategic brilliance, he and his Jedi led the Republic to victory in countless battles, pushing the Mandalorians back.
Revan lured Mandalore the Ultimate and his Mandalorian soldiers into a confrontation on the planet Malachor V. The Mandalorians fought Republic forces above and on the planet. Revan himself engaged Mandalore the Ultimate, the two fighting on the surface of Malachor. Mandalore the Ultimate was cut down by Revan, his mask stolen by the Jedi in an act of both physical and symbolic victory, preventing the Mandalorians from regrouping by selecting a new leader.
The Mass Shadow Generator, a secret weapon developed by engineers for Revan's use, was activated when the Mandalorian fleets got close enough to Malachor. The horrific device tore the fleets apart - both Mandalorian and Republic - ripping them down from space onto the planet itself, killing countless lives and devastating the surface of the planet. The Mandalorians surrendered, their forces decimated, their will and morale broken. Despite what he did, the Mandalorians held a high regard for Revan, for he was the greatest opponent they ever faced.