The film's villain will be
Aquaman's most notable nemesis Black Manta. Manta will be played by Yahya Abdul-Mateen II, and the reason he loathes Aquaman in the comics stems from his the death of his father. The father role will most likely be played by actor Michael Beach, who was seen
earlier this year in a photo Mateen shared on Instagram from the set.
Beach was asked recently if he was playing the role of Manta's father "yes or no?", to which he said, "Yes or No...correct!" It's a sly answer to be sure, but if he wasn't he would have just said no or not at this time. Combined with his earlier appearance, it seems his casting is just going officially unannounced, which makes sense since the role is most likely rather small.