politician who in the last years of the Roman Republic formed the so-called First triumvirate with Julius Caesar (Caesar, Julius) and Pompey (Pompey the Great) to challenge effectively the power of the Senate. His death led to the outbreak of the Civil War between Caesar and Pompey (49–45).

Crassus fled from Rome when Gaius Marius captured the city in 87. As a young officer, he supported Lucius Cornelius Sulla during the civil war (83–82) between Sulla and the followers of Marius, returning to Rome to help Sulla seize power in 82. The hostility between Pompey and Crassus probably originated in Sulla's clear preference for Pompey. Crassus held the praetorship c. 73, and in 72–71 he put down the slave uprising led by Spartacus, although Pompey managed to take the credit. Crassus and Pompey cooperated to pressure the Senate to elect them to the consulship for 70; once in office they overthrew parts of the Sullan constitution.

During the 60s, while Pompey was scoring military victories abroad, Crassus was building a political following at Rome. He used his great wealth—derived largely from the sale of property confiscated by Sulla—to extend credit to indebted senators. The young Julius Caesar was helped in this fashion in 62. In 65 Crassus served as censor.

In 60 Crassus joined with Pompey and Caesar to form the so-called First Triumvirate. Crassus entered this informal coalition partly to effect passage of laws helpful to his business ventures in Asia. From 58 to 56 he supported efforts to neutralize Pompey's power. He and Pompey were reconciled at a meeting of the three leaders at Luca, Etruria, in 56, and in the following year they were both again made consuls. As governor of Syria in 54, Crassus attempted to gain military glory by embarking on an unwarranted invasion of Parthia, to the east. He was defeated and killed at the Battle of Carrhae (see Carrhae, Battle of) in southern Anatolia.