Guan Yu was Liu Bei's sworn brother and a great general under his command, who made countless contributions to Liu Bei's establishment of Shu Han. Later, Liu Bei appointed the Five Tiger Generals: Guan Yu, Zhang Fei, Zhao Yun, Ma Chao, and Huang Zhong, with Guan Yu ranking first among them.
Ma Chao, one of the Five Tiger Generals, was the son of Ma Teng, the governor of Xiliang. After Cao Cao killed Ma Teng, Ma Chao and his cousin Ma Dai raised a massive army from Xiliang and marched on Cao Cao's stronghold of Xuchang to avenge their father. But they fell into Cao Cao's scheme of sowing discord, and after their defeat, Ma Chao fled to Shu and surrendered to Liu Bei.
Guan Yu was a very proud man, and he had long heard of Ma Chao's reputation. At the time, Guan Yu was stationed in Xiangyang, so he deliberately wrote to Zhuge Liang, asking whose character and abilities Ma Chao could be compared to. Zhuge Liang knew Guan Yu's temperament well and understood that Guan Yu was worried Ma Chao might surpass him, so he replied:
"Ma Chao comes from a military family, excels in both civil and martial arts, and is exceptionally brave—a true hero of his time, comparable to Qing Bu and Peng Yue of the early Han, and a match for Zhang Fei. But he can never compare to you, the unparalleled and peerless Lord of the Magnificent Beard."
When Guan Yu received a letter from Zhuge Liang, he was overjoyed
In truth, judging by Ma Chao's martial prowess, he was by no means inferior to Guan Yu; Zhuge Liang said this merely to save face for Guan Yu.
Later, the idiom "Surpassing All Peers" came to describe someone who excels beyond all others, unmatched among their contemporaries.
Source: *Records of the Three Kingdoms*, "Biography of Guan Yu"
Meaning of the Idiom: Later, the Chinese idiom "超群绝伦" came to describe how someone excels beyond all others, unmatched among their contemporaries.