The life of Sulla is one of stark contrast and yet striking similarities to those of Marius, and later, Caesar. Thanks to Sulla's own personal memoirs, which have been lost to history, though preserved through the works of others, such as Plutarch and perhaps Appian, we actually know a great deal about him and the time period. Sulla was cunning and ruthless when necessary, but a brilliant politician and formidable commander as well. While he didn't necessarily begin the "Fall of the Republic", the activities of Sulla were definitely a major contribution.
Sulla was a member of a down and out branch of the patrician Cornelii family. Born into near poverty, compared to other patricians, he spent his youth without hope of restoring the family name. Ancient sources suggest that two timely family inheritances were the catalyst that allowed Sulla to move into politics. With enough financial security to run for public office, and the fortunate (for him) situations with the Germanic Cimbri and the War with Jugurtha, Sulla was granted an opportunity to alter his course in life. Just as Gaius Marius was coming into power of his own, Sulla broke into Roman politics and was elected Quaestor. His next fortunate break was to serve under Marius in Africa.
During the War with Jugurtha, Sulla gained valuable command skills despite relatively minor military action. The war under Marius was definitely working in the favor of Rome, but bottling up the elusive Numidian and destroying his army was a near impossible task. In a brilliant act of diplomacy, Sulla went with authority of Marius to King Bocchus of Mauretania. Bocchus, an ally of Jugurtha, was tiring of the war and was concerned that Rome would eventually win out. Trying to avoid the potential punishment, Sulla was able to convince Bocchus to betray Jugurtha and capture him during a private meeting. The plan worked as suggested, and Sulla soon had custody of the Numidian King, effectively ending the war. While Marius, who was in command, claimed the bulk of the credit, Sulla would, for many years, claim the victory belonged to him. Whatever else had occurred between the men while on campaign, this incident certainly formed the foundation of a bitter rivalry.
Upon their return to Rome, the next threat facing Rome was migrating Germanic Cimbri and Teutones. Marius took command of one force to stop the Teutones, while Sulla joined Marius' rival Catulus in a force to stop the Cimbri. All accounts suggest that Sulla was not only invaluable to Catulus, but that he very well may have saved the Legions and turned the tide in Rome's favor. At the battle of Vercellae in 101 BC, Catulus, with Sulla, defeated the Cimbri and the threat from the Germanics was over. Marius and Catulus, as co-consuls, were honored with a joint triumph, while Sulla's bitterness grew. Returning to Rome from the campaign, Sulla was next elected as Praetor urbanus. While allegations of massive bribery followed him, it didn't stop his political advancement. After his service to Rome, he was appointed as a Propraetor governor of the eastern province of Cilicia.