Lothair, sometimes called Lothair II, d. 869, king of Lotharingia (855–69), second son of Emperor of the West Lothair I. He inherited the region bounded by the Rhine, Scheldt, Alps, and North Sea, which became known as Lotharingia (Lorraine). He was joined to Theutberga, the sister of one of his father's vassals, in an arranged marriage; after the death of Lothair I he repudiated her and married his mistress Waldrada, by whom he had a son. Theutberga appealed to Bishop Hincmar, a counselor to King Charles the Bald of the West Franks (later Emperor of the West Charles II). Charles, Lothair's uncle, hoped to annex Lotharingia if Lothair should die without an heir, which was likely since Theutberga was barren. Hincmar supported Theutberga and with the aid of Pope Nicholas I forced Lothair to reinstate her. When Lothair died suddenly his lands were divided between his uncles, Charles the Bald and Louis the German, by the Treaty of Mersen (870).

Lothair, 941–86, French king (954–86), son and successor of King Louis IV. During the early part of his reign he was dominated by Hugh the Great. Even after Hugh's death he was involved in conflict with the great feudal lords and controlled only a small part of France. He alienated his protector, Holy Roman Emperor Otto II, by his unsuccessful attempt to occupy Lotharingia (Lorraine) in 978. Otto retaliated by invading France. Although Lothair renounced all claims to Lotharingia at a meeting with Otto in 980, he tried to regain it after Otto's death in 983. He died during the campaign and was succeeded by his son Louis V.