Answer
Lü Meng, a general under Sun Quan, played a pivotal role in capturing Guan Yu, a renowned general of Liu Bei. Lü Meng's cunning strategy involved disguising his troops as merchants and launching a surprise attack on Guan Yu's camp. This unexpected assault led to Guan Yu's defeat and eventual capture, significantly weakening Liu Bei's forces and altering the balance of power during the Three Kingdoms period.