The Destroyer is the main antagonist in Final Fantasy Fables: Chocobo's Dungeon. He is really Raffaello when he is possessed by his darkness, a Magic Beast of the Black who was originally the sacred beast to the Oracle of Darkness.
Driven by his lust for suffering, the Destroyer went berserk with intent to destroy the world. In response, the three other Oracles sealed him away by creating a barrier to keep Lostime hidden from the outside world and the Bell of Oblivion, placing its denizens in a state of forgetfulness to ensure the Destroyer would never regain his power. However, the Destroyer placed a monkey wrench into this plan by leaving his Crystal of Dark Destruction, later known in history as Timeless Power, behind in the outside world to attract an ideal pawn unaffected by Lostime to serve him without full knowledge of his actions. Finding such a pawn in Chocobo, the Destroyer assumed the guise of an infant whom the residents regarded as a savior. However, as he has no memories of being the Destroyer, Raffaello developed into his own personality. Each time Raffaello matured upon each guardian defeated, the boy feels more of the Destroyer awakening inside him and having mixed feelings about it. By the time Alexander is defeated, the Destroyer takes full control over the fully grown Raffaello, restoring everyone's memories before assuming his Priest of Darkness form and absorbing Croma's essence. He then challenges Chocobo to chase after him into his lair, the Floating Fortress. During battle, Raffaello tries to fight back his hold, giving Chocobo the upper hand to prevail. As the Destroyer was defeated, both Raffaello and Croma were freed from his hold.
Note: In the first boss battle against him, it is impossible to win.