Gaius Cassius Longinus

Gaius Cassius Longinus (before 85 BC – October 42 BC) was a Roman Senator, a leader of the plot to kill Julius Caesar, and the brother in-law of Brutus.
Biography.
Early life.
Little is known of Gaius Cassius's early life. He studied philosophy at Rhodes and became fluent in Greek. He was married to Tertulla, who was a half-sister of his co-conspirator, Brutus. They had one son.
Quaestorship and Parthia.
Cassius's first office was as quaestor under Marcus Licinius Crassus in 53 BC, and he proved a good military leader. He travelled with Crassus to the province of Syria, and attempted to dissuade him from attacking Parthia, suggesting that they secure a base at the Euphrates. 
Crassus ignored Cassius and led the army into the Battle of Carrhae, during which he also ignored Cassius' plans for strengthening the Roman line. The result was the most famous Roman rout since the Second Punic War.
Cassius managed to save the remnants of the army with the help of Crassus' legate Gaius Octavius. Crassus was killed, but Cassius managed to escape with 500 cavalry and meet up with the surviving legionaries.
For two years afterwards, Cassius governed the province of Syria as Proquaestor, defending the border against Parthian incursions until the new proconsul arrived. The last incursion resulted in the death of the Parthian commander Osaces, and split the Parthian troops. Cicero, then governor of Cilicia, sent Cassius a note of congratulations for the victory.
Civil war.
Cassius returned to Rome two years later. The outbreak of the civil war between Julius Caesar and Pompey the Great saved Cassius from being brought to trial by his enemies for extortion in Syria. Cassius was elected Tribune of the Plebs in 49 BC, and threw in his lot with Pompey, fleeing Italy as Caesar crossed the Rubicon. He met Pompey in Greece, and was made commander of his fleet.
In 48 BC, Cassius sailed his ships to Sicilia where he attacked and burned a large part of Caesar's navy. He then proceeded to harass ships off the Italian coast. News of Pompey's defeat at the Battle of Pharsalus caused Cassius to head for the Hellespont. Cassius was overtaken by Caesar en route, and was forced to surrender unconditionally.
Caesar made Cassius a legate, employing him in the North Africa, but Cassius refused to join in the fight against Cato and Scipio in Africa, choosing instead to retire to Rome.
Conspiracy.
Cassius spent the next two years without office, and apparently tightened his friendship with Cicero. In 44 BC he became "praetor peregrinus" with the promise of the Syrian province for the ensuing year. The appointment of his junior, Brutus, as "praetor urbanus" deeply offended him.
Although Cassius was "the moving spirit" in the plot against Caesar, winning over the chief assassins, Brutus became their leader. On the Ides of March, 44 BC, Cassius urged on his fellow liberators and struck Caesar in the face. He and his fellow conspirators referred to themselves as the "Liberators" "(Liberatores)".
Although they succeeded in assassinating Caesar, the celebration was short-lived. Mark Antony seized power and turned the public against them. In letters written during 44 BC, Cicero frequently complains that Rome was still subjected to tyranny, because the "Liberators" had failed to kill Antony. According to some accounts, Cassius had wanted to kill Antony at the same time as Caesar, but was dissuaded by Brutus.
Post-assassination.
Cassius's reputation in the East made it easy to amass an army from other governors in the area. By this point the Senate had split with Antony and cast its lot with Cassius, making him as governor of Syria. Cassius was now secure enough to march on Egypt, but on the formation of the triumvirate, Brutus requested his assistance. Cassius quickly joined Brutus in Smyrna with most of his army, leaving his nephew behind to govern Syria.
The conspirators decided to attack the triumviri’s allies in Asia. Cassius set upon and sacked Rhodes, while Brutus did the same to Lycia. They regrouped the following year in Sardis, where their armies proclaimed them 'emperor'. They crossed the Hellespont, marched through Thrace, and encamped near Philippi in Macedon. 
Octavian (later known as Augustus) and Mark Antony soon arrived. Cassius planned to starve them out, by using his superior position in the country. However, they were forced into a pair of battles by Antony, in the Battle of Philippi. Brutus was successful against Octavian, and took his camp. Cassius, however, was defeated and overrun by Antony. Cassius, unaware of Brutus' victory, committed suicide. He was mourned by Brutus as "the Last of the Romans". Brutus, like Octavian, was not an experienced military commander and, ten days later, Antony completed the victory. Brutus also committed suicide.
Epicureanism.
"Among that select band of philosophers who have managed to change the world," writes David Sedley, "it would be hard to find a pair with a higher public profile than Brutus and Cassius — brothers-in-law, fellow-assassins, and Shakespearian heroes," adding that "it may not even be widely known that they "were" philosophers".
Cassius converted to the school of thought founded by Epicurus. Arnaldo Momigliano called Cassius' conversion a "conspicuous date in the history of Roman Epicureanism," a choice made not to enjoy the pleasures of the Garden, but to provide a philosophical justification for assassinating a tyrant.
The inconsistencies between traditional Epicureanism and an active approach to securing freedom could not be resolved, and during the Empire, the philosophy of political opposition tended to be Stoic. This circumstance, Momigliano argues, helps explain why historians of the Imperial era found Cassius more difficult to understand than Brutus, and less admirable.
In literature.
In Dante's "Inferno", Cassius is one of three people deemed sinful enough to be chewed in one of the three mouths of Satan, in the very center of Hell, for all eternity, as a punishment for killing Julius Caesar. The other two are Brutus, his fellow conspirator, and Judas Iscariot, the Biblical betrayer of Jesus Christ. (Canto XXXIV) In Shakespeare's play "Julius Caesar" he is depicted as a ruthless manipulator. Caesar says of him, "Yon Cassius has a lean and hungry look; He thinks too much: such men are dangerous". (I. ii. 190-195)