younger son of the Roman general Pompey the Great, and a vigorous opponent of Pompey's Caesarian rivals.

After his father was killed in the Civil War (49–45 BC) against Julius Caesar, Pompeius fled to Spain, where he continued the struggle against Caesar's forces. Following the assassination of Caesar in 44, Pompeius came to terms with Mark Antony (Antony, Mark) and was given a naval command, but in August 43 he was outlawed. For the next several years he ravaged the coast of Italy with his fleet. Occupying Sicily and blockading Italy, he helped Mark Antony against Octavian and, after they renewed their agreement, forced them to make a formal treaty with him, appointing him governor of Sicily and other islands and of Achaea (39). When these promises were not carried out, Pompeius renewed the war and, after some striking successes against Octavian, was decisively defeated by Octavian's friend Agrippa at Naulochus (near Messina, Sicily, 36). He fled to Asia Minor but was captured and executed by the Roman general Marcus Titius.