Belisarius

Belisarius was one of the most notable generals of late antiquity. He started off as a common soldier before somehow wrangling a position as an officer in the personal guard of the Emperor Justin. At the insistence of Justin's ambitious nephew, Petrus Sabbatius, Belisarius was commissioned to raise an experimental regiment of heavy cavalry. He did, and they performed so well that, when Petrus succeeded his uncle and became the Emperor Justinian, he raised Belisarius to high rank and sent him off to reconquer the half of Rome that had been overrun by barbarian hordes. 
     This he did, despite long odds and repeatedly being hamstrung by the imperial court. Africa fell, and the Goths were pushed out of Italy in a bloody war. The crowds in Constantinople went wild. The courageous, competent Belisarius was everyone's hero, and their cheers made Justinian frown. A life lived in the Byzantine halls of power had instilled in the Emperor a long, wide streak of generally justified paranoia, and though Belisarius's ambitions never approached the purple--he was a career soldier through and through, who failed at politics and knew it--Justinian stripped him of his command and sent the court eunuch Narses to finish the job. 
     But the world wasn't done with Belisarius yet. When an army of raiders swept down on the Imperial city out of nowhere, Justinian had no choice but to swallow his pride and ask Belisarius for help. History doesn't record whether or not Belisarius had a smug smirk on his face when he heard, but I wouldn't blame him one bit if he did. Dusting off his armor and sharpening his sword, he formed an ad hoc militia out of retired soldiers, townsmen, and whatever bystanders didn't run away fast enough, trained them into a surprisingly effective team of asskickers, and chased the raiders away. 
     He was repaid for his eleventh hour heroics by being dragged before an imperial tribunal on trumped up charges by his enemies at court (remember that part about failing at politics?) and convicted for corruption and treason. The emperor watched as his greatest general was stripped of rank, property, citizenship, and threatened with a red hot poker for his eyes and a dungeon for a new home before Justinian decided that he couldn't go through with it. He gave Belisarius a full imperial pardon, restored his property and honor, though not his rank, allowed him to retire in comfort, and even built a statue of him for good measure. 
     Emperor and general died within a year of eachother, and their reconquests unraveled less than a generation later. Rome would never be whole again.