The wealthy Roman who joined Caesar and Pompey in the First Triumvirate was Crassus, formally Marcus Licinius Crassus. The alliance brought together Caesar's political drive, Pompey's military prestige, and Crassus's immense wealth and influence.
The First Triumvirate was an informal political agreement formed around 60 BC, not a constitutional office. Crassus helped Caesar overcome financial and political obstacles, while Caesar acted as an intermediary between Crassus and Pompey, who had previously been rivals. Their cooperation helped Caesar win the consulship in 59 BC and advance legislation benefiting Pompey's veterans and Crassus's business allies.
Crassus had made much of his fortune through property dealings connected with the proscriptions under Sulla and became even more famous after helping defeat Spartacus's slave revolt. Despite his wealth, he wanted greater political and military prestige. The alliance was renewed at the conference of Luca in 56 BC, when Crassus and Pompey later became consuls together.
Crassus's death at Carrhae in 53 BC ended the three-man partnership. The remaining rivalry between Caesar and Pompey soon contributed to civil war.