Emperor Taizong of Tang

Li Shimin pushed his father to rebel against the Sui dynasty in 617, then spent years crushing the new Tang regime's most dangerous enemies. In 626 he became emperor - the second of the dynasty but effectively its architect. He expanded the imperial examination system, demanded his officials serve policy over patronage, and led campaigns that broke the Eastern Turks in 630, earning him the title Khan of Heaven. Over the next two decades Tang armies annexed the oasis states of the Tarim Basin and crushed the Western Turkic Khaganate in 657. A rationalist who scorned omens and modified rites to lighten the peasants' load, he surrounded himself with blunt advisors like Wei Zheng and tolerated criticism that would have gotten men killed under weaker rulers. He died in 649, leaving an empire that stretched from Korea to Central Asia and a reputation that became the measuring stick for every throne that followed.