A Kronan made of rocks who narrates his own life in the gentlest voice in these films, including the parts where he is killing people.
Korg is Taika Waititi in a motion capture suit, and he is the clearest signal of what happened to the Thor films when Waititi arrived: they got funnier, and the jokes started coming from characters rather than at their expense.
The trick with Korg is the register. He describes a failed armed uprising, the death of his friends and his own imprisonment in the same mild, friendly tone he uses for everything else, and the films never explain the joke.