Which Roman general fought in the civil war against Pompey?

Julius Caesar is the correct choice because he was a key figure in the civil war against Pompey the Great, which was part of the larger context of the Roman Republic's internal conflicts during the 1st century BCE. This civil war, which began in 49 BCE, was primarily a power struggle between Caesar, who had gained significant military and political power, and Pompey, who was supported by the Senate. Caesar's crossing of the Rubicon River in 49 BCE, famously declaring "the die is cast," marked the point of no return and initiated the conflict.

Caesar's military successes ultimately led to his dictatorship and significant reforms in Rome, altering the landscape of Roman governance. The other figures mentioned played significant roles in Roman history, but they were not involved in this particular civil war against Pompey. Gaius Marius was known for his military reforms and conflicts with Sulla but lived earlier; Scipio Africanus was renowned for defeating Hannibal during the Second Punic War; and Marcus Antonius, while a significant figure in Roman history, primarily aligned with Caesar toward the end of his life, ultimately contending with those who opposed Caesar rather than directly fighting Pompey.