Timaeus

Timaeus was a legendary knight from the city of Atlantis. He also aided Ironheart in the Battle of Atlantis. His name is pronounced as "tim-EYE-us" in the English version of the anime.

Background
Timeaus and the other two legendary knights, Critias and Hermos had resided in the Spirit World, until the city of Atlantis is corrupted by the Orichalcos. Ironheart who was the former ruler of Atlantis had summoned them to the human world to help him thwart Dartz's efforts to wipe out the population of Atlantis in the misled hopes of starting the kingdom anew. However Dartz was able to weaken the knights by trapping them in the forms of dragons.

The Legendary Dragons, had fought alongside rebels from the city of Atlantis and other Duel Spirits against Dartz, Orichalcos Soldiers and The Great Leviathan. Timaeus successfully defeated a number of Orichalcos Soldiers. Dartz however teased his power, striking him with lightning and taking out his eye by means of the Sword of Kings.

The battle concluded with neither side victorious, and Atlantis sinking to the bottom of the sea. The Dragons were sealed in crystal prisons, to be freed if need should ever arise.

Personality
His personality resembles that of Yami Yugi. He doesn't seem to have a rivalry with Critias. However he does have hatred for Dartz because he cutted his left eye.

Appearance
Timeaus, like the other Legendary Knights, is named after one of Plato's dialogues, which are the source of many of the rumors pertaining to Atlantis.

In his human form, Timaeus dons a mix of teal and green armor, and is characteristically missing one eye from a past encounter with Dartz. In this case his left eye that has a scar running down it. Like the other knights, he bears a similar facial expression to his chosen Duelist, Yami Yugi. Timaeus's humanoid color scheme continues into his dragon form, where he is also mostly teal.

Waking the Dragons arc
Yugi Muto and his other-self Yami Yugi were chosen as a Legendary Duelist to wield Timaeus. In a dream, the Yugis are taken to the Duel Monsters Spirit World, where they are taken to Timaeus, trapped in his prison. By removing a sword they set Timaeus free and get the card "The Eye of Timaeus", so that they may Summon "Timaeus" while playing Duel Monsters.

As a card, Timaeus had the ability to combine itself with Yugi's other monsters. He aided Yugi in his Duel against Rafael, but disappeared after Yami Yugi played "The Seal of Orichalcos". After Yugi lost his soul, Yami Yugi tried to summon "Timaeus" against Weevil Underwood, Yami was deemed unworthy after his transgressions in his previous Duel. Yami Yugi came into contact with the spirits of Ironheart and Chris. They helped Yami Yugi recover his self-esteem and ultimately allowed him to summon Timaeus again. Yami Yugi did summoned the dragon such as when he battled Dartz's minions.

When Yami Yugi faced Dartz, he used "Legend of Heart" to change the dragons back to their true forms. Together with Critias and Hermos, Yugi was able to defeat Dartz's "Divine Serpent" and win the Duel.

However The Great Leviathan, was Summoned again. Timeaus took part in the battle against it, this time his side emerged victorious. He along with Critias, Hermos and Dark Magician Girl appeared on the beach to thank Yugi and Yami Yugi before returning to the spirit world.

Ironheart
He gets along with him and follows his orders.

Trivia

 * Timaeus bears a striking resembles to Yami Yugi.
 * He doesn't appear in the manga.
 * He doesn't seem to have a rivalry with his friends.

Voice Actors
all information on Timaeus came from http://yugioh.wikia.com/wiki/Timaeus
 * Japanese : Shunsuke Kazama
 * English : Dan Green