Rupert of the Rhine

Prince Rupert of the Rhine was a military commander, a nephew of King Charles I and cousin of King Charles II of England. He was fighting in English Civil War on the side of the Cavaliers.

He was dashing and handsome, with huge brown eyes, a thin, aquiline nose and a dimpled chin. (PROSE: The Roundheads)

On 26 July 1643, he met the Eleventh Doctor, Amy and Rory in Bristol. He had a poodle called Boye which was used by Parzival to gain influence with the King. Using the influence of Parzival, the opposing side was left stunned, unable to move and speak, while their weapons were collected up. (COMIC: Dog of War!)

In the summer of 1644, Prince Rupert led an 18,000-man strong army that fought against Oliver Cromwell at Marston Moor in the English Civil War. He was soundly defeated. (PROSE: Nightshade, The Roundheads)

He fell out of favour with Charles I after giving up the port of Bristol to the Parliamentarians. The king sent him into exile. (PROSE: The Roundheads)

In December 1648, travelling under the alias Richard Godley with his pet monkey, he was engaged in an attempt to restore Charles I as the king. To this end he hired a Dutch assassin Gustavus van Leeuwenhoek to kill Oliver Cromwell. When the Second Doctor and Ben Jackson prevented the assassination, Prince Rupert fled England. (PROSE: The Roundheads)

Behind the scenes
While Mark Gatiss did not use the title "of the Rhine" in The Roundheads, he stated that Charles I was Prince Rupert's uncle, thereby identifying him beyond any doubt.