Belial is one of the seven Great Evils and is returning to Sanctuary in Diablo 4 Season 8. While deemed only a "Lesser" Evil ...

Some of the previously revealed Evils in Diablo 4 include Duriel, Andariel, and Mephisto. With Belial's introduction, we're now missing only Azmodan, Baal, and, of course, Diablo himself.