Oliver Cromwell ( April 25 1599 â `` September 3 1658 ) was an English military and political leader best known for making England a republic and leading the Commonwealth of England . Oliver Cromwell ( 25 April 1599 â `` 3 September 1658 ) was an English military and political leader best known in England for his overthrow of the monarchy and temporarily turning England into a republican Commonwealth and for his rule as Lord Protector of England , Scotland and Ireland .