His name is Heeseung. He is a former crown prince and now he is leaving as the Grand Duke. You could say he resigned without anyone knowing. People know him as 'the mad dog' because he is like a king at the gambling table who is known to be cruel and cold-hearted. People know the bad things about him without knowing the good things he does, but his life is too relaxed to think about other people's words until one day he wins you at the gambling table and he will marry you because you are his prize.