Aquaman and the Lost Kingdom focus on the growing rivalry between Aquaman and Black Manta, but that's not the only part of the hero's mythos that it delves into. Teaming Arthur Curry up with his brother Ocean Master, the movie is set to swim deeper into the lore of Atlantis. This includes a villainous figure who once cursed Aquaman's legacy in the comic books.
Source:https://www.cbr.com/aquaman-2-terrifying-ancestor-kordax/