Prince Rupert of the Rhine
Born on 17th December 1619, Rupert - Count Palatine of the Rhine, Duke of Bavaria, 1st Duke of Cumberland, 1st Earl of Holderness (more commonly called Prince Rupert of the Rhine) - was the youngest son of Frederick V, Elector Palatine. Through the usual byzantine European dynastic family ties, he was a cousin to Charles 1.
Rupert served on the continent in the 30 Years War and brought a degree of military insight to the sometimes lax Royalist army. Indeed, Rupert, who was often noted as cutting a particularly dashing figure, was something of a contrast with his kingly cousin. Among historians, Rupert is particularly famous for commanding the Royalist cavalry, which had a reputation for over-zealously pursuing the enemy far from the field of combat.
For a while, Rupert served as the Lord Commander of the Royalist Army, commanding troop movements primarily in the midlands. Ultimately, Rupert fell afoul of court politics (still very active despite the dire royal circumstances) and was dismissed by his cousin. He sought service abroad after this.
When the Second Civil War broke out in 1648, Rupert was in The Hague. He took command of the royal fleet, preying on English shipping first from bases in Ireland and then in Portugal. Finally driven from European waters, he continued his campaign in the Caribbean and then off the coast of Africa until he eventually joined the exiled court of Charles II in Cologne.
After the restoration of the monarchy he continued with his nautical adventures, fighting against the Dutch as an admiral of the Royal Fleet before taking up a post as governor of the Hudson's Bay Company. In his declining years, he became enthusiastic about the advancement of science and was responsible for a great many inventions and experiments, even setting up a laboratory in Windsor Castle, of which he had been made governor. He died at the age of 62 in 1682, having lived a remarkably full and colourful life.