Gaius Marius (157 - 86 BCE)
The Constitution stated that Roman Consuls could only serve one out of every ten years. However, Gaius Marius ruled as Consul for seven out of ten years. This may have been due to his military success during three different wars.
To convince men to serve in these wars, Marius promised them land when they returned. The Senate didn't like this but had to agree. Later, Marius increased this reward by promising the soldiers Roman citizenship. This angered the Senate. They refused to honor both of Marius's promises.
Marius defended his reign against an attack by Sulla. Soon after, Marius fled to Africa. When Sulla left Rome for war, Marius returned and seized Rome after a bloody battle.