Tang Taizong (唐太宗) was emperor of the Tang dynasty during Xuanzang's pilgrimage to the west.
Xuanzang was also bestowed the name Tang Sanzang, symbolizing the camaraderie between emperor Taizong and Xuanzang.
Genealogy
Li Shimin (李世民) descends from Chen Baxian (陈霸先) from the paternal side. Chen Baxian had a concubine surnamed Li, and they had a son. Chen Baxian decided to give this son the surname Li. Later, Mao Zedong and Hu Yaobang were inspired by Chen Baxian's actions and gave their daughters the surname Li. Indeed, many people surnamed Li inherit it from their mothers' side. This was especially so when the Mongol and Man people swept through north China.
Anyways, Chen Baxian's son Li migrated north and was captured by Xianbei tribes. After several generations, Chen Baxian's great-great grandsons would father Li Shimin.