King Charles I was the English monarch executed during the English Civil War. His reign was marked by conflicts with Parliament over issues of governance, taxation, and religion. After a series of disputes, the war erupted between the Royalists and Parliamentarians. Ultimately, Charles was defeated and captured, leading to his trial for treason. In January 1649, he was found guilty and subsequently executed, marking a significant turning point in English history. His death symbolized the struggle for parliamentary sovereignty and laid the groundwork for the future constitutional monarchy, ending the notion of absolute rule in England.