Short answers, pulled from the story.
Lucius Cornelius Sulla Felix (138-78 BC) was a Roman general and statesman who became the first man in the late Roman Republic to march an army on Rome and win a civil war. He later revived the office of dictator, carried out sweeping constitutional reforms, and then voluntarily resigned his powers, setting a precedent that figures such as Pompey and Julius Caesar would later exploit.
Sulla was appointed dictator with unlimited powers under the lex Valeria after his victory at the Battle of the Colline Gate in 82 BC, reviving a magistracy dormant since the Second Punic War. His reforms expanded criminal courts with entirely senatorial juries, stripped tribunes of their power to introduce legislation, raised the number of quaestors to twenty with automatic entry into the Senate, and tightened legal controls over provincial governors. He resigned the dictatorship at the start of 80 BC.
Sulla began publishing proscription lists on the 3rd of November 82 BC, starting with roughly 80 names and expanding to hundreds more over the following days. Any person named on the lists was condemned to death without trial, their property was forfeit to the state, and their descendants were barred from civil office for two generations. Killers and informers received rewards, while those who sheltered the proscribed faced penalties.
The tribune Publius Sulpicius Rufus, in a deal with Sulla's rival Gaius Marius, passed legislation transferring Sulla's command against Mithridates VI of Pontus to Marius. Sulla, then consul, responded by leading his army from Nola against Rome itself. He outlawed Marius, Sulpicius, and ten others, and had Sulpicius's legislation annulled on the grounds it had been passed by force.
Sulla crossed into Greece in early 87 BC with five legions, sacked Athens on the 1st of March 86 BC, and defeated the Pontic armies at the battles of Chaeronea and Orchomenus in the summer of 86 BC. He then negotiated peace at Dardanus in autumn 85 BC, requiring Mithridates to return his conquests and pay a war indemnity of two or three thousand talents in exchange for recognition of his position in Pontus.
Sulla was born around 138 BC into a poor branch of the patrician gens Cornelia. After his father's death left him with almost nothing, he spent his youth among actors, comedians, and dancers, writing Atellan farces. He inherited money from his stepmother and his mistress Nicopolis around the time he turned thirty, which allowed him to enter Roman political life. He had no military experience before his first posting as quaestor under Gaius Marius in 108 BC.