Short answers, pulled from the story.
Charles XIV John, born Jean-Baptiste Jules Bernadotte on the 26th of January 1763 in Pau in the province of Béarn, was the first monarch of Sweden's Bernadotte dynasty. He reigned as King of Sweden and Norway from the 5th of February 1818 until his death on the 8th of March 1844. Before becoming Swedish royalty, he had served as a Marshal of Napoleon's French Empire.
An obscure Swedish courtier, Baron Karl Otto Mörner, offered Bernadotte the Swedish succession entirely on his own initiative in 1810, without government authorization. The Riksdag of the Estates formally elected Bernadotte crown prince on the 21st of August 1810 in Örebro. Bernadotte's reputation for fairness toward Swedish prisoners at Lübeck in 1806 had made him known and respected in Sweden before Mörner's approach.
Charles John commanded the Allied Army of the North, which crossed the Elbe and joined the Battle of Leipzig on the 19th of October 1813, bringing fresh troops reinforced by 30,000 Prussians. At a critical moment, entire Saxon regiments defected to his army in response to his proclamation, and Bernadotte was the first Allied sovereign to enter Leipzig. He had also drawn up the Trachenberg Plan, the general Allied campaign strategy, at the conference of Trachenberg earlier that year.
The Treaty of Kiel, signed on the 15th of January 1814, transferred Norway from Denmark to Swedish control after Charles John invaded Denmark and defeated the Danish Army. The treaty fulfilled a key objective he had pursued since joining the Sixth Coalition, as Russia and Britain had pledged to support Norwegian cession to Sweden in exchange for Swedish military participation in the war against France.
In 1834, when relations between Britain and Russia were strained over the Near East Crisis, Charles John sent memoranda to both governments and proclaimed Swedish neutrality in advance. Historians point to this act as the origin of Sweden's long tradition of neutrality. His post-Napoleonic foreign policy consistently prioritized balance among the Great Powers and avoiding conflicts outside the Scandinavian peninsula.
On his deathbed in March 1844, Charles John was heard to say: "Nobody has had a career in life like mine. I could perhaps have been able to agree to become Napoleon's ally: but when he attacked the country that had placed its fate in my hands, he could find in me no other than an opponent." He died on the afternoon of the 8th of March 1844 and was interred at Stockholm's Riddarholmen Church.