The English king executed during the English Civil War was King Charles I. His reign was marked by conflicts between the monarchy and Parliament over issues of governance and royal authority. Following his defeat in the Civil War, he was tried for treason and found guilty. On January 30, 1649, Charles I was publicly executed outside the Banqueting House in Whitehall, London. This unprecedented action demonstrated the limits of monarchical power and marked a critical point in British history, leading to the establishment of the Commonwealth of England.