(c. 157–86 bc), Roman general and statesman, who led the Populares during the civil war of 88–86 bc.

Marius was born at Arpinum (now Arpino). As a young man he served in Spain under the Roman general Scipio Africanus the Younger. In 119 bc he was elected tribune of the people. His marriage to Julia, the aunt of Julius Caesar, improved his social status, but as leader of the popular party he retained his sympathy with the lower classes. After serving as praetor in 115 bc, he returned to Spain, where he waged a successful campaign against the brigands and cutthroats who had been terrorizing the country. He accompanied the Roman general Quintus Caecilius Metellus to Africa in 109 bc. He was elected consul two years later and was vested with the conduct of the war against Jugurtha, king of Numidia. Assisted by his chief aide, Lucius Cornelius Sulla, Marius captured Jugurtha and brought the war to a successful conclusion in 106 bc. The enemies of Marius gave the credit for the victory to Sulla, thereby laying the foundation of the later hatred between the two leaders.

After spending two years in subjugating Numidia, Marius again became (104 bc) consul and advanced northward to oppose the invading Germanic tribes of the Cimbri and the Teutons. He annihilated the Teutons at Aquae Sextiae (now Aix-en-Provence, France) in 102 bc and defeated the Cimbri the following year near Vercellae (now Vercelli, Italy). Marius was considered the savior of his country and in 100 bc was made consul for the sixth time.

When Sulla, as consul, was entrusted with the conduct of the war against the powerful Asian king Mithradates VI in 88 bc, Marius, who had developed a jealous hatred for his patrician rival, attempted to deprive him of his command. Civil war broke out between the partisans of the two leaders. Marius was forced to flee, and Sulla proceeded to Asia Minor to take up his command. Marius then hurried back to Italy, where an uprising of his friends had taken place under Lucius Cornelius Cinna, a bitter opponent of Sulla. Marius and Cinna marched against Rome, which was forced to capitulate. Marius then took his revenge on the aristocracy in a veritable orgy of indiscriminate murder. He had himself and Cinna named to the consulship in 86 bc. By then an old man, Marius died in Rome on January 13 of that year after holding the office for only a few days.