In his human form, Hermos wears red armor. Like the other knights he bears a similar facial expression to his chosen duelist, Joey Wheeler.
His red color scheme follows him into his dragon form.
Hermos has a Duel Monsters card form. The card, "Claw of Hermos", along with its counterparts "The Eye of Timaeus" and "Fang of Critias" are unlike other cards. They have their own set of rules and are color coded blue. Although Monster Cards, the Dragons are played similar to if they were Spell Cards and can combine with other cards. Hermos can combine with monsters to form Equip Spell Cards. It has been shown to combine with five such cards; "Big Bang Blow", "Queen's Knight", "Red-Eyes Black Dragon", "Rocket Warrior" and "Time Wizard" to form "Big Bang Dragon Blow", "Goddess Bow", "Red-Eyes Black Dragon Sword", "Rocket Hermos Cannon" and "Time Magic Hammer".
Hermos and the other legendary knights, Timaeus and Critias resided in the Spirit's World, until Atlantis 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 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 be needed again.
Joey Wheeler was chosen as a Legendary Duelist to wield Hermos. During a Duel with Mai Valentine, he and Yugi were subconsciously taken to the Duel Monsters Spirit World, where they saw Hermos trapped in his prison. By removing a sword Joey set Hermos free and got the card "Claw of Hermos", so that he may Summon "Hermos" while playing Duel Monsters.
As a card, Hermos had the ability to combine itself with monster to create Equip Spell Cards. Joey used it to form "Time Magic Hammer" in his Duel against Mai. He also used it against Rex to create "Red-Eyes Black Dragon Sword", against Valon to create "Rocket Hermos Cannon" and "Big Bang Dragon Blow" and in his second Duel against Mai to create "Red-Eyes Black Dragon Sword" again.
After Joey lost to Mai, Mai had a change of heart stormed off to face Dartz taking the "Hermos" card with her. However she was confronted by Rafael, who defeated her and took the card. When Yugi arrived, Rafael gave him the card, before they dueled. Yugi used it in the Duel to create "Goddess Bow".
When Yugi and Kaiba faces Dartz, Yugi used "Legend of Heart" to change the dragons back to their true forms. Together with Timaeus and Critias, Yugi was able to defeat Dartz's "Divine Serpent Geh" and win the Duel.
However The Great Leviathan, was Summoned again. Hermos took part in the battle against it, this time his side emerged victorious. He, Timaeus, Critias and Dark Magician Girl appeared on the beach to thank Yugi before returning to the spirit world.