Short answers, pulled from the story.
The crisis began on the 10th of December 134 BC with the inauguration of Tiberius Gracchus as tribune. Some historians argue it started when he first issued his proposal for land reform in 133 BC.
Scipio Nasica acted as a private citizen and killed Tiberius Gracchus against the advice of Publius Mucius Scaevola. This assassination occurred in 133 BC after Gracchus attempted to secure a second term as tribune of the plebs.
Octavian was granted the title of Augustus by the Senate in 27 BC marking the beginning of the Roman Empire. The crisis also ended at the assassination of Julius Caesar on the 15th of March 44 BC or when Octavian became the first Roman Emperor.
Gaius Marius served as consul six times consecutively known as his sixth consulship in 100 BC. These consecutive terms violated Roman law which mandated a decade between consulships.
Sulla returned in 82 BC at the head of his army after concluding peace with Mithridates. He defeated the Cinnan faction and forced the Assemblies to make him dictator for an indefinite term.