Lucius II, né Gherardo Caccianemici dal Orso (d. February 15, 1145) was pope from March 12, 1144 until his death.

Born as Gherardo Caccianemici dal Orso in Bologna he became canon at his native city, then cardinal priest of Sta Croce in Gerusalemme , later treasurer of the Roman Church, papa legate in Germany for Pope Honorius II and later for Pope Innocent II. It must be ascribed chiefly to his exertions that Lothair III made two expeditions to Italy for the purpose of protecting Innocent II against the Antipope Anacletus II. Innocent II appointed him papal chancellor and librarian.

His stormy pontificate was marked by the erection of a revolutionary republic at Rome which sought to deprive the pope of his temporal power, and by the recognition of papal suzerainty over Portugal.

In 1144 he met Roger II of Sicily at Ceperano to clarify the duties of Roger as vassal of the Holy See. Lucius was not willing to accept the demands of Roger and rejected them, but Roger forced Lucius to accept his conditions by arms.

The Roman senate, which practically took all temporal power from the pope during the pontificate of Innocent II and was dissolved by Lucius, was resurrected, encouraged by Lucius' defeat. Lucius called unsuccessfully for the help of emperor Conrad III against the senate, and finally marched against them with a small army. This fight was lost by Lucius, too. According to Godfrey of Viterbo he was seriously injured during this battle and died a few days later from his injuries.