Final answer:
In William Shakespeare's play 'Julius Caesar', Casca is the first conspirator to stab Caesar, marking the beginning of the assassination that contributed to the fall of the Roman Republic.
Step-by-step explanation:
In Julius Caesar, a play by William Shakespeare, the first conspirator to stab Caesar was Casca. Although other significant figures like Brutus and Cassius were involved in the plot to kill Caesar, it was Casca who initiated the act that led to Caesar's death on the Ides of March (March 15), 44 BCE. Shortly thereafter, the other conspirators joined in the assassination, which marked a pivotal moment in Roman history, leading to the end of the Roman Republic and the rise of the Roman Empire.