Critias and the other legendary knights, Timaeus and Hermos resided in the Spirit's World, until Atlanis became corrupt by the Orichalcos. Ironheart summoned them to the human world, to help him defeat Dartz, who was trying to wipe out the population of Atlantis and start fresh. However, Dartz weakened the knights by turning them into dragons.
The Legendary Dragons fought alongside rebels from Atlantis and more Duel Spirits, against Dartz, Orichalcos Soldiers and The Great Leviathan.
The battle ended with neither side victorious and Atlantis sunk to the bottom of the sea. The Dragons were sealed in crystal prisons, until they would needed again.
Critias, like 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, Critias wears blue armor. Like the other knights he bears a similar facial expression to his chosen duelist, Seto Kaiba.
In his dragon form, Critias is a dark shade of blue.
Yu-Gi-Oh! Duel Monsters (Anime)
Waking the Dragons arc
Seto Kaiba was chosen as a Legendary Duelist to wield Critias. During his Duel with Alister, he was subconsciously taken to the Duel Monsters Spirit World, where he saw Critias trapped in his prison. By removing a sword he set Critias free and got the card "The Fang of Critias", so that he may Summon "Critias" while playing Duel Monsters.
As a card, Critias had the ability to combine itself with Trap Cards. Kaiba used it to make use of his "Crash Card Virus", which Alister had prevented him from using with 'Royal Decree". He used it in his second Duel against Alister to Summon "Tyrant Burst Dragon" then 'Blue Eyes Tyrant Dragon".
When Yugi and Kaiba faces Dartz, Kaiba combined "The Fang of Critias" with Yugi's "Mirror Force" to Summon 'Mirror Force Dragon". Yugi later used "Legend of Heart" to change the dragons back to their true forms. Together with Timaeus and Hermos, Yugi was able to defeat Dartz's 'Divine Serpent" and win the Duel.
However, The Great Leviathan was Summoned again. Critias took part in the battle against it, this time his side emerged victorious. He, Timaeus, Hermos and Dark Magician Girl appeared on the beach to thank Yugi Muto and Yami Yugi before returning to the spirit world.
Dark Magician Girl
- He doesn't appear in the manga.
- Japanese : Kenjiro Tsuda
- English : Eric Stuart
all information on Critias came from http://yugioh.wikia.com/wiki/Critias