Marius Gaius (155? B.C.-86 B.C.), a Roman army officer and political leader. Marius rose from the ranks of the army to become an officer. He was victorious over Numidia in North Africa, 105 B.C., and repelled a barbarian invasion of northern Italy, 104–101. Marius created Rome's first professional army by using recruits, who were promised land, rather than relying on a militia consisting of conscripted landowners.

Marius served six times as consul during the years 107–100 B.C. He led the populares (people's party) in opposition to the aristocratic Senate. He and Sulla, leader of the aristocrats, commanded Roman armies in the Social War (91–89), a civil war between Rome and other cities in Italy. In 88 war broke out between Marius and Sulla, and Marius was driven into exile. He returned the next year and with the aid of Cinna captured Rome. He was elected consul again just before his death.