Head of State of the United Kingdom: Queen Elizabeth II

Explanation:
Queen Elizabeth II is the current head of state of the United Kingdom. She has been the queen since 1952, following the death of her father, King George VI. Queen Elizabeth II is the longest-reigning monarch in British history, surpassing the previous record held by her great-great-grandmother, Queen Victoria.

Key points:
1. Queen Elizabeth II became the queen at the age of 25, after the death of her father on February 6, 1952.
2. She was officially crowned as the queen on June 2, 1953, in a ceremony known as the Coronation of Queen Elizabeth II.
3. Queen Elizabeth II is the constitutional monarch of the United Kingdom, which means that she holds a largely ceremonial role and does not have any political power.
4. The United Kingdom is a constitutional monarchy, which means that the monarch's powers are limited by a constitution or a set of laws.
5. As the head of state, Queen Elizabeth II performs various ceremonial duties, such as opening and closing sessions of Parliament, giving royal assent to laws, and representing the United Kingdom on state visits and diplomatic trips.
6. The Queen also has other roles and titles, including being the head of the Commonwealth of Nations, an organization of 54 countries, most of which are former territories of the British Empire.
7. Queen Elizabeth II is highly respected and admired by the people of the United Kingdom and around the world for her dedication and service to her country.
8. It is important to note that the head of government in the United Kingdom is the Prime Minister, who is responsible for running the day-to-day affairs of the country. The current Prime Minister is Boris Johnson.

Conclusion:
Queen Elizabeth II is the head of state of the United Kingdom. She has held this position since 1952 and is the longest-reigning monarch in British history. While her role is largely ceremonial, she is highly respected and admired for her dedication to her country.