Born into a French middle-class family in 1763, Jean-Baptiste Jules Bernadotte got into the royal army as a private soldier in 1780 when he was seventeen; as he was apparently a terrific supporter of the French Revolution (q.v.) he got rapid promotion, becoming a general in 1793 when he was thirty. It had taken thirteen years to move upwards from private to cadet to colonel to general. This could only have happened in France, amid the insane atmosphere of the Revolution.
Napoleon Bonaparte promoted him to Marshal at forty-one years old in 1804, and gave him important commands at Austerlitz (q.v., in command of the central reserve) and at Jena in 1806. Here his career seemed to have taken him by surprise for he was almost court-martialled for failure to obey orders. Notwithstanding, his tremendous pursuit of the Prussians to the Baltic Sea redeemed him in Bonaparte’s eyes. He accepted the Prussians’ surrender, as well as that of a Swedish division sent to help them. Now he made his master career move: he treated the Swedes courteously and sent them home with a flea in the ear, and a growing Swedish respect for him!
Bernadotte failed however at the battle of Wagram in 1809 and was relieved of his command by the Emperor himself. He was to return to France in disgrace. Now the Swedes, who had recently lost Finland to Russia, needed a vigorous military figure as their heir apparent, Charles XIII having no surviving children; they offered Bernadotte the position, and Napoleon actually allowed Bernadotte to become Crown Prince! Obviously he was thinking along the lines of Henry II of England, who thought that making his friend Becket Archbishop of Canterbury (q.v.) would make him subservient and easy to handle. Both Henry and Napoleon were sadly mistaken.
Once he was appointed Heir to Sweden Bernadotte put the interests of Sweden first, not those of France. When Napoleon seized Swedish territory in 1812, Bernadotte brought Sweden into the coalition against France and fought with the allies at the battle of Leipzig. It is said that our hero wanted to succeed Napoleon as ruler of France when the latter abdicated, but the other Marshals of France had other ideas, as they saw him (correctly from the French point of view) as a traitor. Nothing abashed, B. returned to Sweden and organised the annexation of Norway to Sweden at the Congress of Vienna.
By 1818 the Private Soldier/Marshal of France was King of Sweden (and Norway) calling himself Charles XIV. He instantly showed he was good at ruling by accepting parliamentary control of taxation, and ensuring that Ministers understood their responsibilities to the elected Diet. He also re-arranged and codified the laws.
The descendants of Jean-Baptiste Jules Bernadotte remain on the thrones of Sweden and Norway.