Though other actors have previously been speculated to be playing the part, according to Batman News, David Thewlis is the actor portraying Ares in this summer’s Wonder Woman.
As it stands now, Thewlis is credited as being in Wonder Woman in an undisclosed role, so it’s certainly possible that the actor could be playing the villain.
The site reports that they have heard from multiple sources that Thewlis is the actor behind the God of War and that the role is a “mix of CGI and practical effects.”
The author speculates that this is why the character has yet to be seen in any trailers or commercials thus far as the post-production team finalizes the CGI for the movie.