Don Joaquin is the first Defender of Earth and appears as a boss in Disgaea: Hour of Darkness. Long ago, before the events of the game, he departed on a quest to slay the Netherworld Overlord and never returned.
During Laharl's journey to reclaim the throne, the party receives a challenge from someone claiming to be the 'Defender of Earth'. Captain Gordon and Jennifer, assuming it is Kurtis, convince the others to accept. It turns out that Don has been living as a ghost in the Netherworld all this time, waiting for a chance to battle the Overlord.
