Who was Guibert of Ravenna, also known as Clement III?

Guibert of Ravenna (c. 1025–1100) was an Italian nobleman who served as the antipope Clement III from 1080 to 1100.1

A key figure in the Investiture Controversy, Guibert served at the German court and was appointed archbishop of Ravenna by Henry IV, Holy Roman emperor. He eventually became the leader of the imperialist faction opposing the reforms of Pope Gregory VII, who subsequently excommunicated him.12

In 1080, a synod convened by Henry IV at Brixen elected Guibert as antipope. After Henry IV successfully seized Rome in 1084, Guibert was enthroned as Clement III and performed the coronation of Henry IV as emperor. He maintained his claim to the papacy throughout the reigns of several legitimate popes, including Victor III and Urban II.12

Please note that this individual should not be confused with the legitimate Pope Clement III, who served from 1187 to 1191.3