Gaius Cassius Longinus (c. 3 October 85 BCE – 3 October 42 BCE) was a Roman Senator, one of the earliest members of the Hidden Ones, a precursor to the Assassin Brotherhood and the brother in-law of Marcus Junius Brutus.
In 47 BCE, Cassius alongside Brutus was recruited by Aya into the Hidden Ones. Intending combat the Order of the Ancients in Rome, they regrouped in the hideout below the Library of Alexandria to make preperations. They later assisted Aya against Roman ships in the Mediterranean Sea before making the journey to Rome and establishing a branch there.
Following Gaius Julius Caesar's promotion to dictator of the Roman Republic, the Hidden Ones recruited the thirty nine Roman senators and began to plot Caesar's assassination, calling themselves Liberatores. On 15 March 44 BCE, Aya, Brutus and Cassius arrived at the Theater of Pompey, intending to carry out the assassination. While Aya went to dealt with Lucius Septimius a member of the Ancients, Brutus and Cassius were tasked to delay Caesar before they could carry on with their plan. After Aya killed Septimius and arrived at the Senate to deliver the first stab, Cassius, along with Brutus and twenty three other senators, followed and stabbed Caesar to death.