Aurelian: 270 - 275
Within a time span of only four years, this former Sirmium peasant drove all the barbarians out and defeated all his rivals. He first forced the remaining Goths to leave north of the Danube. Aurelian began the process of evacuating the province of Dacia, which he considered too hard to defend and subsequently left to the Goths. Then he dealt successfully with the Alemanni, who after being trapped escaped desperately to threaten Rome. In preparation for the future, the emperor ordered that a city walls be built around Rome. The eternal city had not be threatened since the time of Hannibal one thousand years ago, this order was a startling sign of decaying empire. Tetricus had been forced to be declared the emperor in Gaul by his soldiers. He neither wanted to nor asked to be put in the position he was. When the day came that Aurelian marched against him, he deserted his army in the middle of the battle and they were subsequently defeated. Tetricus was forced to return to Rome as a captive of war.
Finally, it became evident that Aurelian had to deal with Palmyra when Queen Zenobia took over Egypt. To keep Rome's grain supply from being cut off, Aurelian immediately landed an army in Egypt and marched up toward Palmyra. Eventually the city had to be destroyed and Zenobia sent back to Rome in chains. For these accomplishments, the senate gave unto him the title "Restorer of the World". After that and a triumph at Rome, Aurelian died while making preparations for a Persian war. Apparently some of his soldiers feared for their own lives and decided to make the first move by killing their master.