Brother Hearthsworn is a skill trainer in Might and Magic VIII: Day of the Destroyer. He can be found in his home in the Ironsand Desert and teaches grandmaster mace.
His services cost 8,000 gold, and the party member must have ten ranks in mace first. Grandmaster mace is only available to Priests of the Sun.
Hearthsworn is one of the people that the party must give a potion of fire resistance to in order to solve the Deliver Fire Resistance Potions quest.