Li Meng 李蒙

In Chapter 9 of the Romance, when the two columns of Zhang Ji and Fan Chou invade Chang'an and Li Jue and Guo Si attack from behind, Lü Bu fights them beneath the city walls without success, and many of his soldiers, fearing his ferocity, surrender to the enemy. A few days later Li Meng and Wang Fang, remnants of Dong Zhuo's faction, act as insiders for the enemy within the city and secretly open the city gates, and the enemy armies of all four columns pour in at once. Unable to hold them off, Lü Bu abandons his family and escapes through the pass, and Li Jue and Guo Si let their troops loose to plunder at will and then kill Wang Yun beneath the tower of the Xuanping Gate. Romance, Ch. 9 §44–48 · 50–51

In Chapter 10 the four men Li Jue, Guo Si, Zhang Ji and Fan Chou write down the titles they want and present them, becoming generals and marquises, and the rest, Li Meng, Wang Fang and others, each become colonels. Romance, Ch. 10 §2–3

When Ma Teng, the Grand Administrator of Xiliang, and Han Sui, the Inspector of Bing Province, lead more than 100,000 troops against Chang'an, declaring that they will punish the traitors, the adviser Jia Xu says that if they only dig deep moats, build high ramparts and hold fast, the enemy's provisions will run out within a hundred days. Li Meng and Wang Fang come forward saying that this is no good plan, and offer to cut off the heads of Ma Teng and Han Sui at once and present them if they are lent 10,000 picked troops; when Jia Xu says that if they fight now they will surely be defeated, they declare in unison that if they lose they will gladly give up their heads, but if they win Jia Xu must give up his. As Jia Xu proposes, Zhang Ji and Fan Chou are stationed on Mount Zhouzhi, and Li Jue and Guo Si give 15,000 men and horses to Li Meng and Wang Fang. The two set off delighted and pitch camp 280 li from Chang'an. Romance, Ch. 10 §5 · 7–8

When Ma Teng and Han Sui revile the two as traitors to the state, Ma Teng's son Ma Chao, just seventeen years old, comes flying out from the ranks. Wang Fang, scorning his youth, meets him in combat and after only a few bouts is speared and falls from his horse. Seeing Wang Fang speared to death, Li Meng rides alone after Ma Chao as he turns his horse to go back, but Ma Chao deliberately pretends not to notice and dawdles, then twists his body to dodge the spear Li Meng thrusts at him, and when the two horses come side by side he reaches out his arm and takes him captive. Ma Teng and Han Sui, pressing their advantage, win a great victory, advance to pitch camp at the pass, and have Li Meng beheaded and his head displayed. Romance, Ch. 10 §9–11

Only on hearing that Li Meng and Wang Fang have both been killed by Ma Chao do Li Jue and Guo Si believe that Jia Xu has foresight, and they simply hold the passes fast and do not come out even when challenged to battle. Sure enough, in less than two months the Xiliang army runs out of provisions and fodder, and when its plan for insiders in Chang'an is also exposed, it withdraws. Romance, Ch. 10 §12–13