Countries with a sovereign monarchy are the United Kingdom, Sweden, Norway, Denmark, The Netherlands, Spain, Belgium, Monaco, Thailand, Japan, Morocco, and Vatican City. Most of the monarchies are hereditary, which means they are passed down from one family to another, usually from father to son, but not in every situation.
The United Kingdom, and fifteen Commonwealth countries, for example, are headed by Queen Elizabeth II. These commonwealth countries were once a part of the vast empire that Britain ruled in the 19th and 20th centuries. Elizabeth is Queen because her uncle, King Edward VIII abdicated the throne. Other countries are both elective and hereditary.
The answer to this question really depends on what is meant by ruled. For example, the United Kingdom is still a monarchy but the queen is mostly just considered the head of state. She really has no political power, the British Parliament makes the laws. But, there are still maybe a handful or so countries where the monarchs do hold some “real” power.
These countries are: Brunei, Swaziland, Saudi Arabia, Bhutan, Monaco, Bahrain, Liechtenstein, United Arab Emirates (UAE) and Oman. It is interesting to note that the UAE is comprised of seven different kingdoms (emirates), each with its own ruler. The two most well-known emirates are Dubai and Abu Dhabi.