Oscar was the only son of French marshal Jean-Baptiste Bernadotte and his wife, Désirée Clary. As Charles XIII & II of Sweden was without heirs, his father was elected Crown Prince of Sweden in 1810 and eleven-year-old Oscar was created Duke of Södermanland. Oscar and his mother moved from Paris to Stockholm where Oscar quickly learned the Swedish language. His mother, however, had difficulty adjusting to the Swedish court and despised the cold weather. She left Sweden in the summer of 1811 and did not return until 1823. Oscar's father eventually succeeded Charles upon his death in 1818 as King Carl XIV John, founding the new Bernadotte dynasty. Seeking to legitimise the new dynasty, Oscar's father had selected four European princesses as potential brides for his son. Oscar eventually married Josephine of Leuchtenberg in 1823 and had five children with her.

During his father's lifetime Oscar served as viceroy of Norway twice, in 1824 and 1833. Oscar was more liberal compared to his father and took progressive views on education, freedom of the press, and penal reform among others, writing and publishing several articles on these subjects. He succeeded his father upon his death in 1844 and continued with his reform plans. Among these reforms was the equal inheritance rights for men and women. He also broke with his father's pro-Russia foreign policy. Later, he introduced new flags and symbols for Sweden and Norway in an effort to show equality between his two kingdoms.

In the 1850s, his health began to rapidly deteriorate, By September 1857, Oscar was paralyzed and his eldest son Carl was declared Regent. Oscar died at the Royal Palace in Stockholm on 8 July 1859 and was succeeded by his son, Carl XV.

Oscar I was born at 291 Rue Cisalpine in Paris (today: 32 Rue Monceau), the son of then French Minister of War, general Jean-Baptiste Bernadotte and Désirée Clary. He was named Joseph after his godfather Joseph Bonaparte who was married to his mother's elder sister, Julie Clary, but was also given the names François Oscar. The latter name was chosen by Napoleon after one of the heroes in the Ossian cycle of poems.

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