Constantine, and not solely due to him being the first Emperor to embrace Christianity, but also because he established the Empire in the East with such firm foundations that it endured another 1100 years. Augustine because he founded it and ushered in almost a badly needed century of internal peace for the Empire. Aurelian, the best of the soldier emperors, who earned the title of Second Founder of the Empire by largely ending most of the chaos of the third century, ending the age of the hundred emperors. Put your picks in the comboxes.
