king of lower Burgundy, or Provence, from 877.

The son of Buvin (or Beuves), Count of Ardennes, Boso was given the governance of Lombardy (876) by his brother-in-law Charles II the Bald, king of the West Franks (France), and received the title of duke. During the minorities of the West Frankish kings Louis III and Carloman, he convoked the bishops of Provence and had them proclaim him their king (Oct. 15, 879). Boso thereafter proceeded to expand his domains. The territory over which he usurped royal authority included not only Provence but many lands to the north, as far as Autun—an enlarged Burgundy.

In succeeding years, especially 880–882, Boso lost many of the marginal northern lands to the French and German Carolingians, who were reestablishing their authority. He was succeeded by his son, Louis, who in 901 became the Frankish emperor Louis III.