The general of the Roman emperor Justinian (527-565CE). Belisarius was famed to never lose a battle.
Justinian allowed Belisarius a great amount of freedom over the military. He exploited this freedom to drastically expand the empire from 527-565CE, defeating the Vandals in North Africa, Spain, and most of Italy.
After Justinian these territories were lost by the Romans due to (1) a drain on taxes to maintain such a large army and (2) repeated rebellions and alliances.<.p>
We know much about Belisarius' conquests from the historian Procopius.