A dictator assumes absolute power for himself and at best is a leader who takes total control of a country that has lost its way. He may well be self-chosen and put into leadership position by a series of bribes, threats and worse. A monarch is a hereditary leader, a king or a queen, the first born or chosen successor to a deceased king. these are historic lines of descent and the monarch is not chosen.
Nor does the monarchy depend upon capability, talent, looks or any other quality except the blood connection. To keep the monarchy 'pure' in the past a monarch from one country would be paired off with a suitable monarchic relative of a friendly country. Europe maintained peace or attempted to by such monarchic ties between their countries. Times have changed to a degree, but not totally!
A dictator and a monarch are similar in that each is the only ruler of their country and neither are elected by votes from the citizens. They are different because a monarch, such as a king, queen, or emperor usually passes the rule to a child, such as a first born son or daughter.
Queen Elizabeth is the current monarch in England and her monarchy is known as a constitutional monarchy because while she is the Head of State, the British parliament makes the laws. Dictators will usually come into power through military force or rebellion. Sometimes dictators pass their rule to someone within their family, for example the Kim family in North Korea and the al-Assad’ family in Syria.