In 265 BC, Li Mu was stationed in Yanmen Commandery and ordered to assume command of Zhao's overall security situation for the northwestern commanderies of Yanshan and Daijun by defending against raids instigated by the Xiongnu and other tribes. He initially adopted an extremely defensive strategy, for which he was accused of cowardice and thereafter replaced by a more aggressive general who was defeated every time he engaged in battle with the Xiongnu. Li Mu was quickly recalled and again placed in charge of defending against the nomads: In 243 BC, Li Mu took over command in the war against Yan and managed to conquer Wusui and Fangcheng. Later, as the threat from Qin increased with the previous ascension of King Zheng, Li Mu turned his focus more towards the western parts of Zhao. However, the State of Zhao was significantly weakened. After having previously suffered utter defeat at the hands of Qin forces led by Bai Qi during, and in the aftermath of, the Battle of Changping in 260 BC, in which Zhao had lost virtually its entire army, most of the core Zhao territories had fallen to Qin. Furthermore, Zhao was diplomatically isolated as the Kingdoms of Wei, Yan, and Han were too weak to offer any kind of support, while Qi and Chu were more willing to see the kingdom extinguished than face the powerful Qin. Nevertheless, Li Mu could still hold out against and compete with the much stronger Qin forces. So while Qin could raid Wei and Han at will, they had a much harder time pillaging in Zhao. In 233 BC, when Qin forces attacked the cities of Chili and Xuan'an, Li Mu erected a fortified camp at Feidi and waited for the Qin general Huan Yi to divide his army and attack one of the divisions. The plan succeeded, and Li Mu defeated the Qin army at Yi'an. He was rewarded with the title of Marquis of Wu'an. A year later, he again defeated the Qin army at Fanwu. Getting rid of Li Mu became a necessity for Qin to conquer Zhao and ultimately to unify China. In 229 BC, in light of Wang Jian's invasion of Zhao, the Qin sent spies to the Zhao court, bribing key courtiers such as Guo Kai and Han Cang in order to convince them to persuade the King of Zhao to replace Li Mu and Sima Shang with Zhao Cong and Yan Ju as generals by alleging that the former were planning a rebellion. The plan succeeded - Li Mu was dismissed from his position and soon thereafter either executed or forced to commit suicide on the king's orders. With Li Mu's death, the fall of Zhao became inevitable. In just a few years' time King Dai would fall and the State of Zhao would fade into history.
In Hara Yasuhisa's Kingdom where he is called Riboku, he was initially seen as a pacifist as shown when he was stationed in northern Zhao, but his experience and tactics were on par with other Warring State rivals. He also has a one-shot manga that Yasuhisa wrote before publishing Kingdom that details his background and youth. He is an excellent strategist, on par with Wang Jian and Lord Changping. He also has an interest in Li Xin's ability in that manga. And he always told his generals to eliminate him to stop the former's growth. In Kingdom, he is represented as a seemingly carefree and friendly man, but holds a scarily intelligent and ruthless side to him that is shown during warfare. In the series, he’s acquired many loyal followers, most notably his bodyguard Kaine/Hai Yin, a commander named Fu Tei/Fu Di, Shun Sui Ju and the great general candidate Kei Sha/Qing She, latter killed by Shin/Xin himself.
