Emperor Xian of Han
Cao Cao died on 15 March 220. His son and successor, Cao Pi, soon forced Emperor Xian to abdicate the throne in favour of himself, ending the Han dynasty. Cao Pi established a new state known as Cao Wei (sometimes known inaccurately as the Kingdom of Wei), and he granted Emperor Xian a noble title – Duke of Shanyang (山陽公). The former Emperor Xian died in 234 and was buried with honours befitting an emperor, using Han ceremonies, and the then emperor of Wei, Cao Rui, was one of the mourners. As Emperor Xian's crown prince was already dead, his grandson Liu Kang (劉康) inherited his dukedom, which lasted for 75 more years and two more dukes, Liu Jin (劉瑾) and Liu Qiu (劉秋), until the line was exterminated by invading Xiongnu tribes in about 309, during the Jin dynasty. This practice of an emperor conferring hereditary nobility on his predecessor, from whom he usurped the throne, was known as "er wang san ke" (二王三恪).
Cao Zizheng
In 220, Cao Zizheng's half-brother Cao Pi became the first emperor of the Cao Wei state after usurping the throne from Emperor Xian, the last emperor of the Han dynasty. The following year, he honoured Cao Zizheng with the posthumous title "Duke Dai of Mei" (郿戴公), and ordered Cao Fan (曹範), a son of Cao Ju, to be Cao Zizheng's heir. In 222, Cao Pi enfeoffed Cao Fan as the Marquis of Pingshi (平氏侯), but changed his title to Marquis of Chengwu (成武侯) in the following year. In 229, Cao Pi's successor, Cao Rui, promoted Cao Fan from a marquis to a duke. Cao Fan died in 235 without a son to succeed him, and was posthumously honoured as "Duke Dao" (悼公). In 236, Cao Rui ordered Cao Chan (曹闡), Cao Fan's younger brother, to be Cao Fan's heir. Cao Chan thus became the new Duke of Mei (郿公). Throughout the reigns of the subsequent Wei emperors, the number of taxable households in Cao Chan's dukedom increased until it reached 1,800.