Original: It was held by Oliver Cromwell (December 1653–September 1658) and his son and designated successor Richard Cromwell (September 1658–May 1659) during what is now known as The Protectorate.
Simplified: It was held by Oliver Cromwell (December 1653 September 1658) and his son Richard Cromwell (September 1658 May 1659) during what is now known as the Protectorate.