Final answer:
Julius Caesar left Octavian, his grand-nephew, most of his wealth and power, which indirectly included authority over Gaul after Caesar's death. Direct governance of Gaul ended when Caesar crossed the Rubicon to march on Rome.
Step-by-step explanation:
The student asked who Julius Caesar left in charge of Gaul. Although the direct successor after Caesar's assassination is not specifically mentioned in the historical texts provided, it is well-documented that Caesar's grand-nephew, Octavian, later known as Augustus, inherited Caesar's wealth and, by extension, his political power following Caesar's death.
However, it was Caesar himself who had established control over Gaul, adding Gallic elites to Roman society and rewarding those who had supported him. In 49 BCE, Caesar chose to cross the Rubicon and march on Rome with his army, effectively ending his direct governance over Gaul and initiating a civil war against Pompey and the Senate.