Guan Yu, born Changsheng in Xie County, Hedong Commandery, adopted the courtesy name Yunchang. After killing a member of a ruling family, he became a fugitive and fled to Zhuo Commandery. There, he met Liu Bei and Zhang Fei. The three swore an oath of brotherhood in a peach garden, pledging to restore stability and serve their country, with Liu Bei as eldest, Guan Yu as second brother, and Zhang Fei as youngest.

He joined Liu Bei's volunteer militia during the Yellow Turban Rebellion, aiding Colonel Zou Jing in suppressing the revolt. His physical prowess and combat skills earned recognition. Alongside Zhang Fei, he protected Liu Bei in crowds and during meetings, sharing close quarters and demonstrating unwavering loyalty through dangers. Guan Yu treated soldiers kindly but showed disdain toward the gentry.

While serving under Cao Cao, Guan Yu guarded Xiapi while Liu Bei resided in Xiaopei. In 200 AD, Cao Cao attacked Xu Province and captured Guan Yu. Cao Cao appointed him Lieutenant General, treating him with great honor. At the Battle of Boma, Guan Yu slew the general Yan Liang, lifting the siege and earning the title "Marquis of Hanshou Village" from Emperor Xian. Despite Cao Cao's generosity, Guan Yu maintained loyalty to Liu Bei. After repaying Cao Cao by defeating his enemies, he departed, leaving behind all gifts and a formal resignation letter. Cao Cao permitted his departure, acknowledging Guan Yu's loyalty to his oath.

Guan Yu reunited with Liu Bei in Jing Province. When Liu Bei fled Cao Cao's forces after the Battle of Changban, Guan Yu organized naval reinforcements, facilitating their escape to Xiakou. Sun Quan's forces later aided them against Cao Cao at the Battle of Red Cliffs. Following Liu Bei's pacification of Jiangnan, Guan Yu was appointed Governor of Xiangyang and General Who Terrifies Criminals, tasked with defending northern Jing Province.

After Liu Bei secured Yi Province, Guan Yu managed Jing Province affairs. He exhibited pride when questioning Ma Chao's abilities; Zhuge Liang assuaged him by praising his superiority. During a medical procedure to remove poison from his arm, Guan Yu calmly ate and drank while a surgeon scraped his bone.

In 219 AD, Guan Yu attacked Cao Ren at Fan Castle. He exploited flooding to defeat Cao Cao's reinforcements, executing General Pang De and accepting Yu Jin's surrender. This alarmed Cao Cao, who considered relocating the capital. Sun Quan, resentful over Guan Yu's rejection of a marriage proposal for his son, exploited internal discord. Guan Yu's subordinates Mi Fang and Fu Shiren defected to Wu after fearing punishment for supply failures. Wu forces captured Jiangling, dispersing Guan Yu's army. Retreating from Fan Castle, Guan Yu was captured and executed at Linju alongside his son Guan Ping.

Guan Yu was studious, often reciting the *Spring and Autumn Annals*. He possessed a tall stature and a distinctive long beard, earning the nickname "Lord of the Magnificent Beard." He wore green robes over armor and wielded the Green Dragon Crescent Blade, a guandao weighing approximately 49 kilograms.

Posthumously, he was deified as "Emperor Guan," "Lord Guan," or "Sangharama Bodhisattva." Revered in Confucianism, Taoism, and Buddhism for embodying *zhongyi* (loyalty-righteousness), temples dedicated to him exist worldwide. He is venerated as a god of war, brotherhood, justice, and wealth. Merchants particularly honor him for inventing ancient accounting methods and upholding integrity.