Emperor Chengzu 明成祖 (1360-1424, r. 1402-1424), personal name Zhu Di 朱棣, the Yongle Emperor 永樂, was the third ruler of the Ming dynasty 明 (1368-1644). He was the fourth son of Emperor Taizu 明太祖 (the Hongwu Emperor 洪武, r. 1368-1398), the founder of the Ming. He was given the princedom of Yan 燕 around modern Beijing 北京, a region that was located in a critical position because it was endangered by raids of Mongolian hordes. In 1390 he undertook a campaign, together with his brother Zhu Gang 晉王棡, the Prince of Jin, against the Mongol leader Nayir Bukha 乃兒不花, who was defeated by the Ming. In the next years Zhu Di continued to assemble military merits.
When his father died in 1399, the oldest surviving grandson of Emperor Taizu, Zhu Yunwen 朱允炆, acceded to the throne as the Jianwen Emperor 建文帝 (posthumously known as Emperor Hui 明惠帝, r. 1398-1402). The latter saw his position critically endangered by the military power of the many princes (Emperor Taizu had 26 sons) and decided to demote five of them to commoners. Zhu Di feared that he, as probably the most powerful, might be the next, and rose in rebellion. He used the pretext to comply with the "ancestral injunctions" (qingjun ze 清君側) to undertake a military campaign to "appease the trouble" (jingnan 靖難). After four years of campaigning Zhu Di's troops stormed the capital Nanjing 南京 (modern Nanjing, Jiangsu), but the Jianwen Emperor died in the flames that devoured the imperial palace. Zhu Di thereupon usurped the throne and assumed the reign motto Yongle 永樂 "Everlasting Joy".
The Yongle Emperor then had to start a propaganda machine that clear him of all doubts of usurpation. At the same time he deprived all princes of his family of their military power, in order to forestall a similar usurpation as he had committed. He killed Qi Tai 齊泰, Minister of War (bingbu shanshu 兵部尚書) and Huang Zicheng 黃子澄, Chamberlain of Ceremonials (taichangqing 太常卿). The Confucian scholar Fang Xiaoru 方孝孺 also suffered the death penalty. Censor-in-chief (yushi dafu 御史大夫) Jing Qing 景清 planned to assassinate the usurper, but he, too, found the death. The Yongle Emperor revoked all legal changes that his predecessor had made. In 1404 he named his son Zhu Gaochi 朱高熾 heir apparent.
Yet he his most famous for his overseas project in which he sent out the eunuch admiral Zheng He 鄭和 to prospect for tributary countries and to demonstrate the political power of Ming China. The seven exploration voyages began in 1405 and only ended after his death in 1433.
In 1408 Emperor Chengzu sent out Išiqa 亦失哈 to found the military commission (dusi 都司) of the "wild" Nurgan Jurchens 奴爾干. The jurisdiction included the region of the rivers Amur, Jinggiri 精奇里江 (today called Zeya, a northery tributary to River Amur), Ussuri 烏蘇里江, Songhua 松花江, and the island of Kuye 庫頁島 (Sakhalin). The emperor undertook five campaigns to destroy the last Mongol claimants of the throne of the Great Khan. The Mongols thereupon split into the Eastern Mongols (Tatars or Dada 韃靼, and Oirats or Wala 瓦剌). He expanded his former princely seat to a new capital, called Beijing 北京 "northern capital". After nineteen years of work, in 1421, the capital of the Ming empire was removed to the north, while Nanjing, the "southern capital", became secondary capital (liudu 留都), with a full parallel administrative structure.
In the cultural field, the Yongle Emperor can be credited with the compilation of the largest encyclopaedia that was produced in China, the Yongle dadian 永樂大典, of which today only a small part survives.
As a factural usurper Emperor Chengzu did everything to propagate the justified character of his rule and exerted a regime of benevolence, particularly in times of natural disasters, when he immediately brought relief to the suffering population. On the other hand he must be charged with the intensification of the use of court eunuchs for administrative matters, and so initiated the domination of castrates at the imperial court for which the Ming period is notorious. Emperor Chengzu did also not lower the burden of corvée labour to be delivered for official works as a kind of liability to the government. The heavy reliance on peasants for official work led to several uprisings, like that of the female leader Tang Sai'er 唐賽兒 in Shandong in 1420.
The Emperor Chengzu fell ill during a campaign against the Mongol noble Arughtai 阿魯臺 and died in Yumuchuan 榆木川 (near modern Dolun 多倫, Inner Mongolia). He is buried in the tomb hill Changling 長陵 and has the posthumous honorific title Emperor Xiaowen 孝文皇帝 and the temple name Chengzu 明成祖. He was succeeded by his son Emperor Renzong 明仁宗 (the Hongxi Emperor 洪熙, r. 1424-1425).