The ruler who initiated the Protestant Reformation in England was King Henry VIII. In the early 16th century, Henry sought to annul his marriage to Catherine of Aragon due to her failure to produce a male heir. When the Pope refused to grant the annulment, Henry broke away from the Roman Catholic Church, establishing the Church of England in 1534 and affirming his authority as its head. This act not only led to religious reforms but also resulted in significant political and social changes across England, paving the way for new Protestant movements and further weakening the Catholic Church's influence.