John Joseph Frederick Otto Zardetti

John Joseph Frederick Otto Zardetti (January 24, 1847 – May 10, 1902) was a Swiss prelate of the Roman Catholic Church. He served as the first bishop of the new Diocese of Saint Cloud in Minnesota in the United States from 1889 to 1894. Zardetti then served as Archbishop of the Archdiocese of Bucharest in what is today Romania from 1894 to 1895. After resigning as archbishop, Zardetti briefly, but influentially served in the Roman Curia with the title of titular archbishop of Mocissus.

According to his biographer Reverend Vincent A. Yzermans, Zardetti played a major role in successfully pushing for Pope Leo XIII's 1899 Apostolic letterTestem Benevolentiae, which condemned the heresy of Americanism. In commenting on Zardetti's role in the letter, Yzermans has commented, "In this arena he might well have had seen his greatest impact on American Catholicism in the first half of the twentieth century in the United States."