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 Cao Mausoleum
During the forum, Lin Kuicheng, a historian and member of the China Federation of Literary and Art Circles, pointed out that Cao Cao should not be referred to as "King Wu of Wei" before 220 CE. After Cao Cao died in March 220 CE, his vassal king title – "King of Wei" – was inherited by his son, Cao Pi, who continued to hold the title until around December when he forced Emperor Xian, the last emperor of the Han dynasty, to abdicate in his favour. Since Cao Cao was buried about one month after his death and his funeral was most likely presided over by Cao Pi, it would be taboo to refer to Cao Cao as "King Wu of Wei" because the "King of Wei" (Cao Pi) was still living then. Furthermore, when Emperor Xian relinquished his throne to Cao Pi, he referred to Cao Pi and Cao Cao as "King of Wei" and "King Wu" respectively in his official abdication edict; Cao Cao was never referred to as "King Wu of Wei" in the edict.