His parentage is in dispute: his mother, Lady Zhen, was Yuan Xi's wife, but she later remarried Cao Pi, the first ruler of Wei.
He devoted many resources into building palaces and ancestral temples, and his reign saw the stalemate between his empire, Shu Han, and Eastern Wu become more entrenched.
This would prove to be a fatal mistake for his clan, as Cao Shuang monopolised power and governed incompetently, eventually drawing a violent reaction from Sima Yi, who overthrew him in a coup d'état (Incident at the Gaoping Tombs).
Cao Rui, a young adult when he became emperor, quickly showed a knack for finding capable officials to empower while maintaining steady control over them.
His father had appointed three regents for him—his distant cousin Cao Zhen, the steady administrator Chen Qun, and the shrewd strategist Sima Yi.
Once Cao Rui became emperor, however, he, while knowing the value of the advice of these senior officials, chose perhaps the best path to deal with them: honoring them and making them regional governors with full authority in the provinces they governed.
Throughout Cao Rui's reign, he showed great diligence in seeking out advice from multiple officials, rather than concentrating on listening to several, before making important decisions.
One immediate threat that Cao Rui had to deal with after he became emperor were attacks from Shu Han's chancellor, Zhuge Liang.
Ultimately, Zhuge's campaigns were futile; after his death in 234, his plan was largely abandoned by his successors Jiang Wan and Fei Yi.
Throughout his reign, he would generally take a similar stance during campaigns against Eastern Wu as he did with Shu Han—head east personally to be close to the theater of the war, while remaining some distance away from the frontlines, which also proved to be effective.
At the time, many frontline officials were on vacation visiting families, so Man Chong requested Cao Rui to call them back to fight Sun Quan.
In 232, Gongsun Yuan's repeated communicated with and sales of horses to Eastern Wu angered Cao Rui, who ordered his generals Tian Yu and Wang Xiong (王雄) to attack Liaodong against Jiang Ji (蔣濟)'s advice; the attacks were not successful, although Tian was able to intercept the Eastern Wu horse-buying fleet and destroy it.
Gongsun, apprehensive of another attack from Cao Wei, sent ambassadors to Eastern Wu to formally submit to its emperor Sun Quan.
(Part of the Eastern Wu troops were able to escape and eventually returned home with the assistance of Goguryeo, a rival of the Gongsuns.)
Gongsun then declared himself the Prince of Yan and entered into alliances with the Xianbei tribes to harass Cao Wei's borders.
Almost immediately after Cao Rui ascended the throne, he started out large scale palace and temple-building projects.
Part of it was to be expected—the Luoyang palaces had been remnants of the ones not destroyed by Dong Zhuo, and the temples were needed for the cults of his ancestors.
However, he went beyond the minimally required, and continued to build temples and palaces throughout the rest of his reign, severely draining the imperial treasury.
In 237, he further moved many of the magnificent statues and monuments that were commissioned by Emperor Wu of Han from Chang'an to Luoyang, costing great expenses and lives.
He loved Empress Mao dearly, and a number of her relatives, including her father and brother, became honored officials (but without actual powers).
In September that year, when Cao Rui was attending a feast hosted by Consort Guo, Consort Guo requested that Empress Mao be invited to join as well, but Cao Rui refused and further ordered that no news about the feast is to be given to Empress Mao.
[13] Even before his setting of his own temple name, Cao Rui was recorded to be involved in odd behaviour in events regarding the traditions and customs of his day.
On 3 August 229, Cao Teng was posthumously honoured as "Emperor Gao of Wei" (魏高帝),[14] becoming the only eunuch in Chinese officialdom to have this honor.
[16] Cao Rui also insisted that the funeral rites used be those for an adult woman and that court officials were to don mourning clothing; Chen Qun wrote a formal submission to advise the emperor.
A male relative of Empress Mingyuan, Guo De (郭德), was declared to be the deceased couple's child; his surname was changed to "Zhen" and he was made Marquis of Pingyuan, inheriting the princess's title.