The Smile could be a Warlock with an Old One Pact...or he could be something worse. I don't really have preconceptions about his true nature. He longs, as his master longs, for the primordial days of old, when the land was bare of life and everything lived in the sea; subject to it's will. But his defining trait is that he has fun with his job...he has a personable aspect where he genuinely seems to like people. Of course, what he's actually enjoying is the prospect of seeing them all drown, but it's all steps in the process.
So the charismatic thing feels warlocky, but he need not be human as long as he can pass for human. Its worth pointing out that any warlock can select a constantly-active 'Disguise Self' invocation too.