Aithra (RotTs)

Aithra was the Titan of the Sky and the secret son of Gaia and Ouranos, being the youngest and described as the most powerful next to Kronos, Aithra first met Kronos during the last Years of the First Olympian War and fell in love, when the Olympians defeated Kronos and chopped him into pieces they refused Rhea's demands for her to continue as Queen of the Gods and she fell into Aithra's hands who murdered her using Kronos' scythe on the Titan King's last command.

Aithra was eventually hunted down and sealed in a Diamond Casket created in the Undersea Forges overseen by Poseidon, sealed with Stygian Iron Locks crafted by Hades and bound with chains of lightning magicked by Zeus, the Chamber he was sealed in changed every so often as to stop a potential return of the Titan threat but by the modern era the Casket and its chamber had become a part of the Labyrinth - one of the hardest to navigate locations in the world.

Trivia

 * Aithra was the Greek word for the sky, usually translated "the bright sky".