The Act of Supremacy was a law passed by the English Parliament in 1534 during the reign of King Henry VIII. This act declared the king as the Supreme Head of the Church of England, effectively breaking away from the authority of the Pope and the Roman Catholic Church. It marked the beginning of the English Reformation, allowing for the establishment of a separate Anglican Church. The act required all subjects to recognize the king's supremacy, leading to significant religious and political changes in England. Those who refused to accept this authority faced penalties, including imprisonment or execution, as seen in the case of Thomas More.