Zhu Xi (1130-1200), also known as Zhuzi, was a major Song dynasty philosopher and commentator. He was a Confucian scholar who became one of the most significant Neo-Confucians in China.

Zhu Xi was born in what is today Youxi County in Fujian province, where his father was serving as an official, but his home town is considered to be Wu Yuan, now in the northeast corner of Jiangxi province, but then part of Huizhou, a district just south of Huangshan. He spent many years teaching in the Wuyi Mountains on the modern Fujian/Jiangxi province border, and is also particularly associated with two Confucian academies, the Yuelu Academy in Changsha and one at his retreat by the White Deer Grotto in Lushan, northwest of Poyang Lake.

Zhu Xi considered the earlier philosopher Xun Zi to be a heretic for departing from Confucius's beliefs about innate human goodness. Zhu Xi contributed to Confucian philosophy by articulating what was to become the orthodox Confucian interpretation of a number of beliefs in Daoism and Buddhism. He adapted some ideas from these competing religions into his form of Confucianism. He argued that all things are brought into being by two universal elements: vital force (qi), and law or rational principle (li). The source and sum of li is the Tai Ji, which means Great Ultimate. According to Zhu Xi, the Tai Ji causes qi to move and change in the physical world, resulting in the division of the world into the two energy modes (yin and yang) and the five elements (fire, water, wood, metal, and earth).He did not hold to traditional ideas of God or Heaven (Tian). He did not promote the worship of spirits and offerings to images. He disagreed that the souls of ancestors existed, believing instead that ancestor worship is a form of remembrance and gratitude.

Zhu Xi and his fellow scholars codified what is now considered the Confucian canon of classics: the Four Books, consisting of the Analects of Confucius, the Mencius, the Great Learning, and the Doctrine of the Mean.

During the Song Dynasty, Zhu Xi's teachings were considered to be unorthodox. As a result, his ideas led to his being dismissed several times from official positions. But after he died, his teachings were to dominate Confucianism. Life magazine ranked Zhu Xi as the forty-fifth most important person in the last millennium. He was also influential in Japan, where his followers were called the Shushigaku school.