Oliver Cromwell was not a Monarch but an English military and political leader and later Lord Protector of the Commonwealth of England, Scotland, and Ireland. As such his name did appear on coins. The actual monarch was Charles I, whom Cromwell was key in having executed. Also in this category are 'Commonwealth' coins. These were issued between 1649 and 1660. They had no portraits, instead showing the Cross of St George and the Harp of Ireland. The inscriptions were in English rather than Latin so not as to be seen as associating with the Catholic Church.

1651 Sixpence - Commonwealth Mintage: N/A