Gigameth, whose real name is Garuda, is one of the villains from Final Fantasy III.
Gigameth worked as the advisor of King Gorn of Saronia. He actually was a fiend known as Garuda, being disguised as a human to manipulate the king and take over his kingdom. After the flow of time is restored by the Warriors of Light, Gigameth starts mind-controlling King Gorn, who orders his soldiers to fight each other for no reason at all. And if anyone tried to question him he would order the person to be executed for treason. When the king's son, Prince Alus, tried to question the King, he temporarily broke free of the spell, ordering his son to be expelled from the castle, so Gigameth would not harm him.
The Warriors of Light eventually arrive at Saronia, but their airship is accidentally bombarded. They find Alus in the pub, where he is being picked by some bullies. After helping Alus, they decide to help him to end whatever is happening. The king invites them to sleep at the castle, but during night he enters their room and attempts to kill Alus. Everyone awakes, and Gigameth orders him to finish the job, but the king breaks free from the spell and kills himself. Gigameth becomes furious and reveals his true form to fight the Warriors of Light. He is slain by them, and peace is restored to the kingdom.
Final Fantasy VII
Final Fantasy XIV
Final Fantasy Crystal Chronicles: Echoes of Time
Final Fantasy Chrystal Chronicles: My Life as a King