Gaius Marius was a very influential leader in Rome. In his childhood he was said to have found an eagles nest with seven baby eagles in it that would represent his seven years elected as consul. He gained an army by capturing a Numidian leader, Jugurtha. Talking to the people he became very popular and through his military reforms he gained military power.
Lucius Sulla was at one point Gaius Marius' right hand man. He fought in the Social Wars, and gained a very loyal army. He attempted to lower taxes for the people and was a populari. When the threat of Mithradates, the king of Pontus, became too great the Senate elected Sulla to go and defeat Mithradates.
When Gaius Marius heard that Sulla was the general elected by the Senate to defeat Mithradates he was enraged. He took his army and marched straight to the Senate and slaughtered them. Sulla heard news of this and came back to fight Marius but Marius retreated. When Sulla left a second time Marius again returned to Rome and killed more senators. Sulla returned a second time scaring off Marius who later died of natural causes.