Anankos

Anankos (ハイドラ, Hydra in the Japanese version) is the true antagonist of Fire Emblem: Fates, revealed in the game's third route.

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The dragon and king of the hidden kingdom of Touma, he has a hatred of people and inflicts pain on them due to a forgotten debt of gratitude. He is neither a dark or light dragon and controls water. During the first two routes of the game, he poses as the sacred mystical dragon of Nohr and controls it in secret through his familiar, who is disguised as King Garon after killing him.

He resurrects Sumeragi and has him act as his agent as the Hooded Man that assassinates Mikoto with Ganglari. On the third route he also resurrects Mikoto, sending her to kill the Avatar.

He is revealed to be the true father of the Avatar.

Etymology
Anankos may come from the ancient Greek word ἀνάγκη (ananke), meaning "destiny" or "fate". This could hint at both the title and the structure of the game, revolving around the Avatar's choice from which the three storylines begin. Even though it is less common, an other meaning of the same word is "blood bond", which could refer to the relationship between the Avatar and Anankos.

In Greek mythology, Hydra is a serpent-like water monster which possessed many heads and for each one cut off it grew two more. It was slain by Heracles during the second of the Twelve Labours.