When Empress Dowager Deng died, Emperor An (r. 106125 AD) was convinced by the accusations of the eunuchs Li Run () and Jiang Jing () that Deng and her family had planned to depose him. An dismissed Deng's clan members from office, exiled them and forced many to commit suicide. After An's death, his wife, Empress Dowager Yan (d. 126 AD) placed the child Marquess of Beixiang on the throne in an attempt to retain power within her family. However, palace eunuch Sun Cheng (d. 132 AD) masterminded a successful overthrow of her regime to enthrone Emperor Shun of Han (r. 125144 AD). Yan was placed under house arrest, her relatives were either killed or exiled, and her eunuch allies were slaughtered. The regent Liang Ji (d. 159 AD), brother of Empress Liang Na (d. 150 AD), had the brother-in-law of Consort Deng Mengnu (later empress) (d. 165 AD) killed after Deng Mengnu resisted Liang Ji's attempts to control her. Afterward, Emperor Huan employed eunuchs to depose Liang Ji, who was then forced to commit suicide.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): Which person plotted to overthrew the regime of Empress Dowager Yan?
Sun Cheng