Oliver Cromwell?
Cromwell was a politician (Member of Parliament, first for Huntingdon, then for Cambridge) and didn’t become a military man until he joined up after the English Civil War had started. So he was no more a ‘military ruler’ than George Washington (actually less, because George was already in the British redcoat military before the war against Britain and before he became president - he used to toast the King in the Officer’s Mess prior to the secession)