Count Lennart Bernadotte, originally Prince Gustaf Lennart Nicolaus Paul of Sweden, Duke of Småland, was born at the Royal Palace in Stockholm to Prince Wilhelm of Sweden and his wife Grand Duchess Marie Pavlovna of Russia. His paternal grandfather was King Gustav I of Sweden and his maternal great-grandfather was Tsar Alexander II of Russia. His parents' arranged marriage was unhappy and ended in divorce when he was five years old. He remained in Sweden in his father's custody and Grand Duchess Marie returned to her homeland and later escaped the Russian Revolution to Paris. He studied horticulture and ecology, and also pursued filmmaking and photography. In 1932, over his family's objections, he married Karin Nissvandt, a commoner with whom he had four children, and forfeited his royal titles. He took the family name of Bernadotte, and went to work turning his small family island of Mainau on Lake Constance in Germany into a beautiful botanical park and opened it to the public as a tourist attraction. In 1951 he was given the title Count of Wisborg by Grand Duchess Charlotte of Luxembourg in recognition of his efforts.
He served as president of the German Horticultural Society for 30 years. In 1972, after a divorce from his first wife, he married his assistant, Sonja Haunz, 35 years his junior, with whom he had five more children. In the 1980s, Mainau and everything on it was entrusted to the Lennart Bernadotte Foundation.