Ra Devil

Ra Devil is the leader of the Black Moon and main antagonist of Final Fantasy: Legend of the Crystals. Robotic to a certain degree, he is determined to have god-like powers, he is trying to steal the four crystals and has taken Cid's brain to further his goals.

Story
Before the actual events of the story, Ra Devil stole Cid's brain from his grave since it was the only thing left in the world with knowledge of the crystals. However, Cid's grandson Mid, who was their greiving, caught Ra Devil defiling his grandfather's grave and was killed as a result. Ra Devil used the knowledge from Cid's brain and used it to steal the fire, water and earth crystals and now has his eyes set on the wind crystal.

When the heroes figure out that Ra Devil is after the wind crystal, which is currentlyt residing within Linaly, they decide to travel to the black moon and stop him. Realising that the only way to get to the black moon is with a Wind drake, they race to the spire where the wind drake's reside, only to be attacked by Ra Devil's robotic forces on the way. At the tower, Ra Devil constructs a monster out of stone and kidnaps Linaly to the black moon, with the party taking the wind drake to rescue her.

On the black moon, Ra Devil uses the power of the crystals to become Deathgyunos, a horrible abomination that wants to destroy the world. After a constant barrage of attacks, Deathgyunos is defeated not once, but twice, and presumably Ra Devil along with it.