That same trailer also showed Huston’s character overseeing the development of a more destructive poison gas to be used during World War I. Ares has been one of Wonder Woman’s primary foes for decades, and using him in a movie set during The Great War is a great narrative choice.
This isn’t the first time it’s been reported that Ares is Wonder Woman’s main antagonist.
However, the Wonder Woman trailer released in November highlighted Danny Huston’s character as the main threat, so it wouldn’t be unreasonable to assume it’s him.
That said, considering that he feeds off humanity’s conflict, it’s peculiar that he would want to kill all the humans in the DCEU, even with that jealousy boiling within him.