Charles XIV John (Swedish: Karl XIV Johan; born Jean Bernadotte; 26 January 1763 – 8 March 1844) was King of Sweden and Norway from 1818 until his death. In modern Norwegian lists of kings he is called Charles III John (Norwegian: Karl III Johan). He was the first monarch of the Bernadotte dynasty.

Born in Pau in southern France, Bernadotte joined the French Royal Army in 1780. Following the outbreak of the French Revolution, he exhibited great military talent, rapidly rising through the ranks, and was made a brigadier general by 1794. He served with distinction in Italy and Germany, and was briefly Minister of War. His relationship with Napoleon was turbulent; nevertheless, Napoleon named him a Marshal of the Empire on the proclamation of the French Empire. Bernadotte played a significant role in the French victory at Austerlitz, and was made Prince of Pontecorvo as a reward. Bernadotte was, through marriage to Désirée Clary, brother-in-law to Joseph Bonaparte, and thus a member of the extended Imperial family.

In 1810, Bernadotte was unexpectedly elected the heir-presumptive (Crown Prince) to the childless King Charles XIII of Sweden, thanks to the advocacy of Baron Carl Otto Mörner, a Swedish courtier and obscure member of the Riksdag of the Estates. He assumed the name Charles John and was named regent, and generalissimo of the Swedish Armed Forces, soon after his arrival becoming de facto head of state for most of his time as Crown Prince. In 1813, following the sudden unprovoked French invasion of Swedish Pomerania, Crown Prince Charles John was instrumental in the creation of the Sixth Coalition by allying with Tsar Alexander and using Swedish diplomacy to bring warring Russia and Britain together in alliance. He then authored the Trachenberg Plan, the war winning Allied campaign plan, and commanded the Allied Army of the North that defeated two concerted French attempts to capture Berlin and made the decisive attack on the last day of the catastrophic French defeat at Leipzig.

After the War of the Sixth Coalition, Charles John forced King Frederick VI of Denmark to cede Norway to Sweden, leading to the Swedish–Norwegian War of 1814 where Norway was defeated after a single summer's conflict. This put Norway into a union with Sweden, which lasted for almost a century before being peacefully dissolved in 1905. The Swedish–Norwegian war is credited as Sweden's last direct conflict and war.Upon the death of Charles XIII in 1818, Charles John ascended to the thrones. He presided over a period of peace and prosperity, and reigned until his death in 1844.