Yung Wei - As Crown Prince

As Crown Prince

Late in 643, Emperor Taizong issued an edict to select beautiful women among good households to serve as Li Zhi's concubines. However, after Li Zhi declined such treatment, Emperor Taizong cancelled the edict. However, during his years as crown prince, he was said to have favored his concubine Consort Xiao, having two daughters (the later Princesses Yiyang and Gao'an) and one son (Li Sujie) with her, much to the chagrin of his wife Crown Princess Wang, who was childless and jealous for Consort Xiao. Three other concubines of his bore his other sons Li Zhong, Li Xiao (李孝), and Li Shangjin (李上金).

Around the same time, however, Emperor Taizong also became concerned that Li Zhi, who was considered kind but weak in character, would not be strong enough to be an emperor, and secretly discussed with Zhangsun Wuji the possibility of making another son by his concubine Consort Yang (daughter of Emperor Yang of Sui), Li Ke the Prince of Wu, crown prince. Zhangsun repeatedly opposed the idea, and Emperor Taizong did not carry this out.

In 645, when Emperor Taizong launched a campaign against Goguryeo, he took Li Zhi with him to Ding Prefecture (定州, roughly modern Baoding, Hebei) and then left Li Zhi there to be in charge of logistics, before heading to the front himself. He also left senior officials Gao Shilian, Liu Ji, Ma Zhou, Zhang Xingcheng, and Gao Jifu to assist Li Zhi. After the campaign ended in failure later that year, as Emperor Taizong was leading the army back from the front, Li Zhi went to meet him at Linyu Pass (臨渝關, now Shanhai Pass). Emperor Taizong suffered an injury during the campaign, and Li Zhi was said to have, as Emperor Taizong's conditions were getting worse, sucked the pus out of his wound, until Emperor Taizong recovered somewhat. In 646, with Emperor Taizong still recovering, he transferred some of the imperial authorities to Li Zhi. Li Zhi stayed at the imperial palace and attended to Emperor Taizong in his illness. That year, when Emperor Taizong was due to visit Ling Prefecture (靈州, roughly modern Yinchuan, Ningxia) to meet with a number of tribal chiefs who were formerly vassals of Xueyantuo—which had collapsed under Tang and Huige attacks earlier that year—he was set to take Li Zhi with him, but at Zhang's suggestion left Li Zhi in charge at Chang'an instead, to allow Li Zhi to become more familiar with the important affairs of state in his absence. After Emperor Taizong returned from Ling Prefecture, he retained for himself the authorities over imperial worship, state guests, military, the commissioning of officers of higher than the fifth rank, and executions, and transferred all other authorities to Li Zhi.

In 647, a commoner named Duan Zhichong (段志沖) submitted a petition to Emperor Taizong, asking him to pass the throne to Li Zhi. Li Zhi, concerned that Emperor Taizong might be offended, was worried and grieving, and Zhangsun suggested that Duan be executed. Emperor Taizong did not take offense and did not punish Duan or Li Zhi. Meanwhile, Li Zhi began to build a Buddhist temple named Daci'en Temple (大慈恩寺) in commemoration of his mother Empress Zhangsun, and the temple was completed in 648.

In 649, while at the summer palace Cuiwei Palace (翠微宮, in the Qin Mountains), Emperor Taizong was gravely ill, and he, while impressed with Li Shiji's abilities, was concerned that Li Shiji was too able and would not submit to Li Zhi. He stated to Li Zhi:

Li Shiji is full of ability and wisdom, but you had done him no favors, and it may be difficult for him to be faithful to you. I am going to exile him now. If he leaves immediately, promote him to be Pushe and trust him after I die. If he hesitates, execute him.

He then demoted Li Shiji to the post of the commandant of Die Prefecture (疊州, roughly modern Gannan Tibetan Autonomous Prefecture, Gansu). Li Shiji, realizing what was happening, after receiving the order, departed without hesitation.

As Emperor Taizong's illness was getting more serious, Li Zhi continuously attended to him and wept constantly, often going without food, which touched Emperor Taizong greatly. Emperor Taizong entrusted Li Zhi to Zhangsun and Chu Suiliang, and then died on 10 July, 649. Initially, Li Zhi was so mournful that he could not carry out any actions other than holding onto the necks of Zhangsun and Chu. Zhangsun, while mourning himself, reminded Li Zhi that he was now in charge of the empire and must act accordingly. Zhangsun also ordered that Emperor Taizong's death not be announced for the time being, and then, the next day, accompanied Li Zhi back to Chang'an. Zhangsun issued several edicts in Emperor Taizong's name—including making Yu Zhining, Zhang, and Gao Jifu chancellors. Two days later, Emperor Taizong's death was officially announced. On 15 July, Li Zhi took the throne (as Emperor Gaozong).