Martin Zigmar is the commander of HOLY, the unit in charge of policing native Alter users on the Lost Ground. Martin Zigmar is an American immigrant into Japan and was the first known Alter user, though he's never actually used his Alter.
Zigmar does however use his Alter late in the series. His Alter is called "Alter Alias", and exists as two parts; a metal alloy that covers his upper chest and arms, and a separate Alter form "Alias". Alter Alias uses highly compressed air to act as both a shield and powerful shockwaves. But because Zigmar's Alter was heavily refined, using it causes him to rapidly age, going from an early twenties to an elderly man in a single battle.