Short answers, pulled from the story.
Emperor Xuanzong of Tang, personal name Li Longji, was an emperor of the Tang dynasty of China who reigned from 712 to 756. His reign of 44 years was the longest of any Tang emperor. He was born on the 8th of September 685 and died on the 3rd of May 762.
The An Lushan rebellion began in winter 755 after years of tension between An Lushan, the general commanding the empire's most elite troops, and the chancellor Yang Guozhong. Yang Guozhong surrounded An's mansion in Chang'an and had his staff arrested and executed. An, in fear and anger, rebelled from Fanyang, quickly capturing the eastern capital Luoyang.
Yang Guifei, personal name Yang Yuhuan, was originally the wife of Xuanzong's own son, Prince of Shou Li Mao. Xuanzong arranged for her to become a Taoist nun, gave Li Mao a new wife, and brought her secretly into the palace as his senior-ranking concubine, known as Yang Guifei. She and her extended family accumulated enormous wealth and political influence, with her cousins and sisters becoming some of the most powerful figures in Chang'an by 748.
On the 21st of July 710, Xuanzong led a coup against Empress Dowager Wei, who had gained control after the sudden death of Emperor Zhongzong and was believed by traditional historians to have poisoned him. Xuanzong conspired with Princess Taiping, several officials, and three imperial guard officers whose men had been alienated by Empress Wei's nephews. The conspirators killed Wei Bo, Gao Song, and other Wei allies, then stormed the palace; Empress Wei was beheaded while fleeing to an imperial guard camp.
The Kaiyuan era, spanning 713 to 741, is regarded as one of the golden ages of Chinese history. Under Xuanzong's early reign it was a period of political stability, social peace, and economic prosperity, with advances in education, literature, music, painting, sculpture, and religion. Capable chancellors including Yao Chong, Song Jing, and Zhang Yue made government efficient and principled during this period.
On the 14th of July 756, Xuanzong fled Chang'an southward toward Jiannan Circuit. The following day, his imperial guards killed Yang Guozhong and forced Xuanzong to order the death of Yang Guifei. His son Li Heng was declared Emperor Suzong on the 12th of August 756. Xuanzong returned to Chang'an on the 17th of January 758, formally yielded the throne to Suzong, and spent his final years under house conditions at Xingqing Palace until his death on the 3rd of May 762.