Aquaman is the highest grossing movie that DC has ever seen, so it was far from a shock when a sequel was given the green light. Aquaman 2 may be on the way, but it's still a pretty long way off, so there's little we know about it beyond the fact that Aquaman will be in it. However, it looks like the first movie's main antagonist could be returning as well.
Aquaman saw Arthur Curry defeat his half-brother, Orm, also known as Ocean Master. However, while most comic book movie bad guys end up dead by the time the credits role, Orm was only taken prisoner by the new king. That means that actor Patrick Wilson has much greater odds than your average big bad of returning in the sequel, and it seems that could very well happen, as Wilson recently revealed he's been talking to Aquaman director James Wan about the sequel and Orm's place in it. According to Wilson...
I’m slightly briefed [on Orm-related matters]. I just throw a little dart here and there. I’ll say, ‘So, what about this?’ and [James Wan will] say, ‘Well, this is what I’m thinking.’ I can tell you that even his concepts for Aquaman 2 are pushing it even further.
Patrick Wilson may only be "slightly briefed" on what's going on with Aquaman 2, as he tells THR, but the fact that he's briefed at all is telling. If information related to the character of Orm is even being considered it means there's a pretty good chance Patrick Wilson will be back in Aquaman 2. He could return as the sequel's main villain or simply appear in a cameo, but one way or another, it sounds like he'll appear.
It shouldn't be too shocking that Patrick Wilson might find himself back in the Aquaman franchise. Wilson and director James Wan are frequent collaborators, having been involved in the Conjuring franchise before Aquaman. One wonders if Ocean Master would have survived the first Aquaman if he'd been played by anybody else. By keeping him alive, Wilson and Wan can work together on yet another movie.
For some reason I'm having flashbacks to something like Thor: The Dark World when I think about how Ocean Master could fit in a sequel. Perhaps Aquaman and Orm will find themselves in an uneasy partnership in the next movie. Some new threat comes along that Arthur Curry, having not lived below water, isn't equipped to deal with, but Orm has information or abilities that Aquaman needs to fight the threat.
Of course, it will be some time before we have any idea what we're going to get from Aquaman 2. The sequel is set for a December 2022 release date, so it's going to be three years before we actually see what James Wan comes up with, and there's plenty of time for that plan to go through a lot of changes.