Like Alm's base class, the Fighter class, the Hero class is exclusive to him in Gaiden and Echoes and is essentially the game's equivalent of the Great Lord promotion for a main series Lord. Aesthetically, the class changes very little aside from adding a shield to Alm's arm, though he gains a new Status screen image. Alm cannot change into a Hero until Celica has encountered Halcyon, who then Promotes Alm immediately in Gaiden or grants the ability to promote the next time he visits a Shrine in Echoes.
The Hero class gives Alm the new ability to wield a Bow, giving him the ability to counterattack at range. Statwise, the Gaiden/Echoes version of Heroes is very combat oriented boasting impressive growth rates for Strength, Speed, Skill, and Defense. The classes most notable trait, however, is the 150% growth rate of HP, meaning that Alm is guaranteed to get at least 1 point of HP raised each level. It also boasts the highest HP Cap of all playable classes with 52 HP at its maximum. As with many classes in Gaiden, Resistance is a weak point for the class, as any Magical attack on him can inflict severe damage, though his Speed and Skill should allow him to dodge more often than not, mitigating some of this threat.
The Hero class has the highest max HP (182) class base out of any class in the series, a trait shared with class it promotes from and the Dark God class. Due to the way the game handles class bases vs character bases, it is impossible to make use of the Hero class's base.
The Hero class is the only class in Gaiden that can use multiple types of physical weapons.
The Hero class shares it's name with the promotion of Mercenaries in other Fire Emblem Games and Ike's base class in Fire Emblem: Radiant Dawn. However, the 2nd tier Hero Class wields axes instead of a bow and Ike's Hero Class doesn't even wield axes.