Zhou Gong 周公, the Duke of Zhou, personal name Ji Dan 姬旦 (therefore called Zhou Gong Dan 周公旦), was the brother of the founder of the Zhou dynasty (11th cent.-221 BCE), King Wu of Zhou 周武王 (11th cent. BCE). Both were the sons of King Wen of Zhou 周文王.
After the foundation of the Zhou dynasty, Ji Dan was first enfeoffed with Zhou 周 (near modern Baoji 寳雞, Shaanxi), later with Lu 魯. Only two years after the conquest of the kingdom of Shang 商 (16th-11th cent. BCE), King Wu fell sick and ordered his brother Dan to succeed him to the throne. But the Duke refused, had the royal order stored in a golden coffer (jinteng 金縢) and installed King Wu's oldest son Song 誦, later known as King Cheng 周成王, as successor.
The Duke himself acted as regent and proclaimed edicts in the name of the king. The moment of King Wu's death posed an imminent threat to the young dynasty, because a lot of nobles rebelled against the dynasty, and some family members doubted the sincerity of the Duke of Zhou. The Lords of Guan 管 and Cai 蔡, brothers of the Duke, claimed that he usurped the throne. But the proof of his justified regency was kept inside the golden coffer, as history goes. Together with Wu Geng 武庚, the son of the last king of Shang, Lord Guan 管叔 and Lord Cai 蔡叔 rebelled against the Duke of Zhou. The were joined by a lot of other nobles, especially from the southeast (for example, Yan 奄, Pugu 蒲姑, the Xu barbarians 徐戎, the Huai barbarians 淮夷, Xiong 熊 or Ying 盈 or 贏).
In a military campaign lasting for three years, the Duke of Zhou and Duke Shi of Shao 召公奭 were able to put down the rebellion and consolidated the reign of the Zhou dynasty.
Returned to the capital Zhongzhou 宗周 (near modern Xi'an 西安, Shaanxi), the Duke of Zhou reorganised the fiefs of the Zhou kingdom. Two thirds of the fiefs were bestowed to members of the royal family and families loyal to the Ji family 姬, while members of the house of Shang and their allies were transferred to distant fiefs where they could not pose a threat to the central kingdom. Lord Kang 康叔 was enfeoffed with Wei 衛, and Weizi 微子, a son of late King Zhou 紂 of the Shang dynasty 商 (17th-11th cent. BCE), with Song 宋.
The Duke of Zhou had a new, secondary capital established in the east, called Chengzhou 成周 "Completion of the Zhou" or Luoyi 雒邑 (modern Luoyang 洛陽, Henan). He took residence in Chengzhou and governed the eastern part of the kingdom, while the Duke of Shao governed the western part from the primary capital Zongzhou.
When the new capital was sacred by King Cheng, the Duke rendered to him the royal seals and withdrew from government. After his death, he was buried in Bi 畢 near Zongzhou, although he had wished to be enterred in the eastern capital.
His descendants inherited the fief of Zhou, as Dukes of Zhou, and the younger line the fief of Lu, the home state of Confucius 孔子. The Duke of Zhou was therefore highly venerated by the Confucians, not only as ancestor of the ducal house of Lu, but also because the Duke of Zhou was seen as a cultivated inventor of state rituals and etiquette.
The Shangshu dazhuan 尚書大傳 lists the merits of the Duke of Zhou: he appeased the rebellion, pacified the Shang, brought down the unruly lords, established the protection of the central region, built the secondary capital, formed state rituals and ritual music, and finally gave back the rule into the hand of King Cheng.