Final answer:
Aulus Vitellius, a Roman senator, became emperor after Nero's regime ended, ruling for eight months during the Year of the Four Emperors before he was deposed.
Step-by-step explanation:
The question asks about a particular senator in Gaul who attempted to overthrow the emperor Nero. The answer is c) Vitellius. Aulus Vitellius was a Roman senator and later became emperor during the fall of Nero's regime.
The period following Nero's death in 68 CE is known as the Year of the Four Emperors, a tumultuous time during which Vitellius was emperor for eight months before being deposed. He was not directly involved in a conspiracy to overthrow Nero while Nero was alive but benefited from the ultimate overthrow instigated by the revolt in Gaul and Hispania.