Gaius Cassius Longinus, Roman politician (d. 42 BC)
Gaius Cassius Longinus (c. 86 BC – 3 October 42 BC), often referred to as simply Cassius, was a Roman senator and general best known as a leading instigator of the plot to assassinate Julius Caesar on 15 March 44 BC. He was the brother-in-law of Brutus, another leader of the conspiracy. He commanded troops with Brutus during the Battle of Philippi against the combined forces of Mark Antony and Octavian, Caesar's former supporters, and committed suicide after being defeated by Mark Antony.

Cassius was elected as a Tribune of the Plebs in 49 BC. He opposed Caesar, and eventually he commanded a fleet against him during Caesar's Civil War: after Caesar defeated Pompey in the Battle of Pharsalus, Caesar overtook Cassius and forced him to surrender. After Caesar's death, Cassius fled to the East, where he amassed an army of twelve legions. He was supported and made Governor by the Senate. Later he and Brutus marched west against the allies of the Second Triumvirate.

He followed the teachings of the philosopher Epicurus, although scholars debate whether or not these beliefs affected his political life. Cassius is a main character in William Shakespeare's play Julius Caesar that depicts the assassination of Caesar and its aftermath. He is also shown in the lowest circle of Hell in Dante's Inferno as punishment for betraying and killing Caesar.