Otto III (980 - January 23, 1002) was the fourth ruler of the Saxon or Ottonian dynasty. He was elected king of Germany in 983 on the death of his father (Holy Roman Emperor Otto II)

Shortly after his coronation, Henry II, deposed Duke of Bavaria, seized him in an attempt to procure the regency, but in May 984 he was forced to return Otto to his mother, Theophanu, who served as regent until her death in 991. Otto II's mother, Adelaide of Italy then served as regent until Otto III reached his majority in 994.

Otto attempted to revive the glory and power of ancient Rome with himself at the head of a theocratic state. In 996, he came to the aid of Pope John XV at the pope's request to put down the rebellion of a Roman nobleman named Crescentius II . He was declared King of Lombardy at Pavia, but failed to reach Rome before the Pope died. Once in Rome, he engineered the election of his cousin Bruno of Carinthia as Pope Gregory V, the first German pope, and the new pontiff crowned Otto emperor on May 21, 996. Upon Otto's departure from the city, Crescentius deposed Gregory and installed John XVI as pope, but Otto returned to Italy and retook the city in 998, executing Crescentius and reinstating Gregory.

Otto made Rome the administrative center of his empire and revived elaborate Roman customs and Byzantine court ceremonies. He took the titles "the servant of Jesus Christ," "the servant of the apostles," and "emperor of the world." When Gregory V died in 999, he arranged for his former tutor, Gerbert of Aurillac, to be elected pope as Sylvester II. The next year, he made a pilgrimage to the tomb of Adalbert of Prague at Gniezno and founded the archbishopric of Poland.

A minor rebellion by the town of Tibur in 1001 ended up being his undoing. He retook the town, but spared the inhabitants, which made the people of Rome mad because Tibur was a rival they wanted destroyed. This led to a rebellion in February that drove Otto from the city. He withdrew to Ravenna and beseeched his cousin Henry IV, Duke of Bavaria, for military aid, but he died before Henry could arrive. Henry succeeded him as king of Germany (and later as emperor) as Henry II.