Short answers, pulled from the story.
Lucius Cornelius Cinna was a four-time consul of the Roman republic who lived from before 130 BC until early 84 BC. He led an armed uprising against his co-consul Gnaeus Octavius in 87 BC and then dominated Roman politics for the next three years.
Lucius Cornelius Cinna was killed by his own mutinying troops early in 84 BC. The mutiny broke out at Ancona as he tried to move his army across the Adriatic Sea to fight Sulla.
Lucius Cornelius Cinna and his co-consul Gnaeus Octavius clashed over enrolling Rome's new Italian citizens into all thirty-five voting tribes. Cinna backed the plan publicly, while Octavius opposed it. Their dispute escalated into armed conflict known as the Bellum Octavianum, which Cinna won after being expelled from Rome and returning with an army.
Gnaeus Octavius was killed by a squadron of Cinna's cavalry commanded by Gaius Marcius Censorinus after refusing to flee the city. Censorinus then presented Octavius' severed head to Cinna, the first time a Roman consul's head had been displayed as a trophy to another Roman.
Gaius Marius, the exiled Roman general, allied with Cinna and helped him besiege and capture Rome in 87 BC. Marius was elected consul alongside Cinna for 86 BC but died just thirteen days into his seventh consulship, possibly of pneumonia.
Lucius Cornelius Cinna's elder daughter married Gaius Julius Caesar, the future dictator and consul of 59 BC, probably during Cinna's second consulship in 86 BC. This marriage connected Cinna's family directly to Caesar's political rise.