Alamar has Resurrection as a starting spell, which is one of most powerful spells in the game. This fact makes Alamar a valuable hero for all factions except Necropolis. In addition, Alamar starts with Scholar and Wisdom, which is a useful combination, that makes him a "walking Mage Guild" quickly. Three level-ups is minimum for Alamar to have Expert Scholar and Advanced Wisdom, which enables him to teach fourth level spells (including his Resurrection) to any hero capable of learning them.
Black Dragons are immune to Resurrection.