Rupert's varied and numerous scientific and administrative interests, combined with his considerable artistic skills, made him one of the more colourful public figures in England of the Restoration period.

[2] Frederick's mother, Countess Louise Juliana of Nassau, was daughter of William the Silent and half-sister of Maurice, Prince of Orange, who as stadtholders of Holland and other provinces were the leaders of the Dutch Republic.

[8] Rupert was almost left behind in the court's rush to escape Ferdinand's advance on Prague, until courtier Kryštof z Donína (Christopher Dhona) tossed the prince into a carriage at the last moment.

The Palatinate cause was a popular Protestant issue in England, and in 1637 a general public subscription helped fund an expedition under Charles Louis to try to regain the electorate as part of a joint French campaign.

In August 1642, Rupert, along with his brother Prince Maurice and a number of professional soldiers, ran the gauntlet across the sea from the United Provinces, and after one initial failure,[34] evaded the pro-Parliamentary navy and landed in Newcastle.

[36] Rupert's reputation continued to rise and, leading a sudden, courageous charge, he routed a Parliamentarian force at Powick Bridge, the first military engagement of the war.

[45] However, Prince Rupert lacked the social gifts of a courtier, and his humour could turn into a "sardonic wit and a contemptuous manner": with a hasty temper, he was too quick to say whom he respected and whom he disliked.

[56] Rupert responded by making his way across Parliamentary held territory to the King at Newark with Prince Maurice and around a hundred men, fighting their way through smaller enemy units and evading larger ones.

[67] Towards the end of the war, practices were changing for the worse across all sides; a rebellious Leicester was retaken by the Prince in May 1645, and no attempt was made to limit the subsequent killing and plunder.

[73] Rupert's military employment was complicated by his promises to the Holy Roman Emperor that had led to his release from captivity in 1642, and his ongoing commitment to the English Royalist faction in exile.

After a three-week siege, Rupert took the powerful fortress of La Bassée through quiet negotiations with the enemy commander—an impressive accomplishment, and one that won him favour in French court circles.

Discipline continued to deteriorate and Rupert had to intervene personally several times, including defusing one group of mutinous sailors by suddenly dangling the ringleader over the side of his vessel and threatening to drop him into the sea.

[82] One of the obstacles that this plan faced was the growing strength of the Parliamentary fleet and the presence of Robert Blake, one of the finest admirals of the period, as Rupert's opponent during the campaign.

[84] Rupert sailed to Lisbon taking several prizes en route,[85] where he received a warm welcome from King John IV, the ruler of recently independent Portugal, who was a supporter of Charles II.

[89] Instead he encountered a late summer storm, leading to the sinking of the Constant Reformation with the loss of 333 lives—almost including Rupert's brother, Prince Maurice, who only just escaped[90] — and a great deal of captured treasure.

[95] In 1654, Rupert appears to have been involved in a plot to assassinate Oliver Cromwell, an event that would then have been followed by a coup, the landing of a small army in Sussex, and the restoration of Charles II.

[97] After his quarrel with the Royalist court in exile, Rupert travelled to Heidelberg to visit his brother Charles Louis, now partially restored as Elector Palatine, where the two had an ambivalent reunion.

To make matters worse, Charles Louis had been deprived of half the old Palatinate under the Peace of Westphalia, leaving him badly short of money, although he still remained responsible under the Imperial laws of apanage for providing for his younger brother and had offered the sum of £375 per annum, which Rupert had accepted.

Rupert appears to have told a range of associates that he had conceived of the mezzotint process through having watched a soldier scrape the rust from the barrel of his musket during a military campaign.

He produced a few stylish prints in the technique, mostly interpretations of existing paintings, and introduced the form to England after the Restoration, though it was Wallerant Vaillant, Rupert's artistic assistant or tutor, who first popularised the process and exploited it commercially.

[118] Rupert acquired his own apartments in the castle, which were recorded as being "very singular" with some decorated with an "extraordinary" number of "pikes, muskets, pistols, bandoliers, holsters, drums, back, breast, and head pieces", and his inner chambers "hung with tapisserie, curious and effeminate pictures".

[142] Rupert had a characteristic style as an admiral; he relied upon "energetic personal leadership backed by close contact with his officers";[143] having decided how to proceed in a naval campaign, however, it could be difficult for his staff to change his mind.

[144] Rupert played a key part in the conferences held by the Duke of York in 1665 to review tactics and operational methods from the First Anglo-Dutch War, and put these into practice before the St James Day battle.

Rupert allied himself with Lord Shaftesbury on matters of foreign policy, but remained loyal to King Charles II on other issues,[124] and was passionate about protecting the royal prerogative.

[152] The Count de Gramont described Rupert as "brave and courageous even to rashness, but cross-grained and incorrigibly obstinate... he was polite, even to excess, unseasonably; but haughty, and even brutal, when he ought to have been gentle and courteous... his manners were ungracious: he had a dry hard-favoured visage, and a stern look, even when he wished to please; but, when he was out of humour, he was the true picture of reproof".

[171] Rupert also focussed on naval inventions: he devised a balancing mechanism to allow improved quadrant measurements at sea,[170] and produced a diving engine for retrieving objects on the ocean floor.

[170] He also invented an improved method for manufacturing shot of varying sizes in 1663, that was later refined by the scientist Robert Hooke, one of Rupert's Royal Society friends during the period.

Rupert became involved with her during the late 1660s, leaving his previous mistress, Frances Bard, with whom he had a son, Dudley; although Hughes appears to have held out from reciprocating his attentions with the aim of negotiating a suitable settlement.

[178] Hughes rapidly received advancement through his patronage; she became a member of the King's Company by 1669, giving her status and immunity from arrest for debt, and was painted four times by Sir Peter Lely, the foremost court artist of the day.

[180] Hughes lived an expensive lifestyle during the 1670s, enjoying gambling and jewels; Rupert gave her at least £20,000 worth of jewellery during their relationship, including several items from the Palatinate royal collection.