Here is an exerpt from Wikipedia:
Prince Gong (1833~1898) was the sixth son of the Daoguang Emperor (1782-1850). His mother was the Imperial Consort Jing (1812-1855), who later became the Imperial Dowager Consort Kang-Ci, and was made posthumously Empress Xiao Jing Cheng. She was the daughter of a Mongol official in the government, from the Borjigid clan (the descendants of Genghis Khan).
In February 1850, Emperor Daoguang was dying, so he ordered to reveal the secret edict of succession:Yixin was made Prince of the First Rank Gong while his older half-brother Yizhu was proclaimed heir to the throne, which he ascended the following month as the Xianfeng Emperor. Prince Gong did not play a major role during the reign of Xianfeng, as his brother was suspicious of him and kept him at bay. His mother, the concubine Jing, the highest ranking surviving concubine of Emperor Daoguang (whose empresses were all dead already), was not made an Empress Dowager, but merely a Dowager Concubine, which Prince Gong bitterly resented.
Prince Gong's disgrace actually became his good fortune when, in 1860, in the middle of the Second Opium War, Emperor Xianfeng left him behind in Beijing to negotiate with the approaching British and French armies who had invaded northern China, while the court was fleeing to the Rehe Traveling Palace, 230 km./140 miles northeast of Beijing. Prince Gong negotiated the Convention of Peking and thus obtained a position of great influence due to his newly acquired credit with the Western Powers and his control of the militia in Beijing. On August 22, 1861, the Xianfeng Emperor died in Rehe. His only heir, a 5-year-old son of the Noble Consort Yi, ascended to the throne as the Tongzhi Emperor. Xianfeng, on his deathbed, had designated a group of eight senior Manchu officials, led by Sushun, to be regents in the new emperor's minority.
However, Noble Consort Yi was deeply suspicious of Sushun and the influence he had over the late emperor and conspired with Prince Gong to launch a coup. Prince Gong played the essential role in the ensuing struggle, as he had the troops capable of tilting the balance in favor of the Noble Consort Yi and her party or in favor of the eight regents. In November 1861, after secretly meeting the Noble Consort Yi and deciding to side with her, he carried out the Xinyou Coup. The regents, who were accompanying the Xianfeng Emperor's body back to the Forbidden city, were intercepted upon arrival. Palace guards arrested the regents. The two opposing princes among the regents were forced to commit suicide, Sushun was beheaded, and the other five regents were stripped of their titles.
The Noble Consort Yi became co-regent under the name Empress Dowager Cixi, along with the less politically involved Empress Dowager Ci'an, ruling behind the curtain (a court official required that the two co-regents, both women, attend imperial audiences behind a curtain). Prince Gong was named prince-regent and appointed to a variety of important posts in the government, including the powerful Grand Council.
In 1861, Prince Gong established the Zongli Yamen, which functioned as the Qing Empire's de facto foreign ministry. As the long-time head of the Zongli Yamen, Prince Gong was responsible for much of the reforms of the early Self-Strengthening Movement. He founded the Tongwen Guan in 1862 for Chinese scholars to learn foreign languages and technology.
Prince Gong, with the support of the two dowagers, remained the central power figure in China until the 1880s, but he was demoted after being accused of being rude in front of the dowagers.Under this was actually a more profound reason: his relations with Cixi deteriorated since 1869, when he caused the execution of a favorite eunuch of Cixi. Besides, Gong had himself aspired to be the sole regent, in the mold of Dorgon, but Empress Dowager Cixi was unwilling to give up power. He lost considerable prestige and his title of prince-regent after the two chastisements by Cixi, before finally being discredited during the Qing defeat in the Sino-French War (1884-85). He was then overshadowed by his younger half-brother the 1st prince Chun, who had closer ties with Empress Dowager Cixi (for being father of Guangxu Emperor).
In 20th century China, Prince Gong was for a long time vilified as the man who sold the country to the Western powers.In recent years, however, he has been rehabilitated and is now recognized as a great statesman, on par with Li Hongzhang, especially when compared to his brother the hapless Xianfeng Emperor. Alive, he was admired by Westerners with whom he had close contacts, and still keep much of this credit in Western historical circles.
Prince Gong was somehow a tragic figure. He was by every means much more competent than his brother Yizhu, yet, Yizhu was made Emperor instead of him and there is a popular story about why this could happen. It is said that their father, the Daoguang Emperor, decided to test these two sons when his health was shattering. Yizhu (the later Xianfeng Emperor)'s tutor taught him that as he was far more inferior than Yixin in competence, it would be better for him to show more 'benevolence and love' (a notion required for rulers by Confucianism). One day, Daoguang Emperor took these two boys for hunting, Yixin managed to kill and capture a lot of preys while Yizhu began to weep. When asked why by his father, Yizhu replied, 'It's the mating season for deers, I feel it such a cruel conduct to kill female deers. ' Daoguang was greatly impressed. On another occasion, Daoguang Emperor first called Yixin and asked him how he would run the country after the passing away of his father, Yixin answered comprehensively and intelligently with great eloquence; when Yizhu was called and being asked the same question, however, he began to weep again. This time he said that he could not bear the thought of his Emperor father dying, that he hoped that his father could live a life of longevity. Daoguang Emperor was genuinely moved. Though that he knew Yixin was more intelligent and capable, he still passed the throne to Yizhu, whom he thought to be affectionate and loving, while in fact Yizhu was to some extent a hypocrite and by no means fit to become Emperor.
Prince Gong devoted the rest of his life modernizing China and negotiating with foreign powers. Yet he was judged unfairly by both comtemporaries and posterity for quite a long time, saying that he had been 'kowtowing' to foreign powers. However, his mild attitudes towards the foreigners are perfectly understandable when taken into consideration that China was in such a backward state and thus was no military rivalry to foreign powders.
Besides implementing industrialization with the support of Cixi, Prince Gong would also establish the Imperial Translator's College, subject to Zong Li Ya Men (equivalent to Foreign Ministry, also established by him) which marked the beginning of formal foreign language teaching in China.
His political influenced shattered during his later life due to suspicion from Cixi. Before his death in May, 1898, it is said that he transmitted these words to Guangxu Emperor, half self life experience and half warning, 'It's not easy to push forward reform in China.' The impulsive and naive Guangxu Emperor, however, didn't seem to care about what his uncle said. Only several days after Yixin's death, the edict for thorough reform was promulgated.