King Charles I of England reigned from 1625 until his execution in 1649. He faced challenges from Parliament due to his belief in the divine right of kings and conflicts over the limits of his power. His reign was marked by the English Civil War, pitting Royalists against Parliamentarians. Charles was captured, tried, and convicted of treason, becoming the only English monarch to be executed. His death led to the establishment of the Commonwealth under Oliver Cromwell. Charles I is remembered for his struggle for absolute monarchy and his ultimate downfall.