Oliver Cromwell was an English military and political leader who played a key role during the English Civil War in the 17th century. Born in 1599, he initially served as a member of Parliament and later became a general in the Parliamentary army. Cromwell was instrumental in the defeat of the royalist forces loyal to King Charles I. After the war, Cromwell helped establish the Commonwealth of England, a republican form of government. He became the Lord Protector in 1653, ruling until his death in 1658. His leadership was marked by significant military campaigns and controversial policies, including strict Puritan reforms.