Eons ago, the Karathen came to inhabit the Hidden Sea. Sometime before the 11th century, King Atlan of Atlantis exiled himself there due to causing the sinking of Atlantis, alongside his trident, eventually dying.
A millennium later, in the 1990s, Atlanna incidentally found the Hidden Sea, after having been sentenced to the Trench. She was trapped here as the maelstrom is a one-way portal without the true heir wielding the Trident of Atlan.
Decades later, she saved Mera, who was accompanied by Atlanna's son, Arthur, from a pliosaur-like creature. They embraced, reunited, before Arthur went on to take the trident from Atlan's body. The Karathen warned him against it, not being the first to have attempted it, but Arthur used his powers to talk back to the creature, allowing him to take the trident, as well as Atlan's armor. Assisted by the Karathen, they all broke out, finding themselves in the midst of a battle in the Kingdom of the Brine.
- Unidentified Plesiosaur (Presumably Plesiosaurus or Elasmosaurus)
- Unidentified Pliosaur (Presumably Liopleurodon or Kronosaurus)
- The Hidden is heavily implied to be Skartaris, a hollow world inhabited by prehistoric creatures like dinosaurs and woolly mammoths, as well as mythical creatures like elves, dwarves, trolls, goblins, dragons, sorcerers and witches.