Records of the Three Kingdoms
Deng Ai, courtesy name Shizai, was from Jiyang in Yiyang. He stammered as a youth and referred to himself as “Ai, Ai.” Sima Yi liked his views on military colonies and the ground of Longyou. For years Deng Ai faced Jiang Wei in the west.
In the invasion of 263, Zhong Hui attacked Hanzhong and Jian’ge and was held by Jiang Wei. Deng Ai led a side force through the mountains from Yinping, came out at Jiangyou, broke Zhuge Zhan at Mianzhu, and reached Chengdu. Liu Shan surrendered. After the conquest Zhong Hui accused Deng Ai of rebellion. When the edict arrived, Deng Ai and his son were killed at Mianzhu by the officer sent to arrest them.
Romance of the Three Kingdoms
The novel accepts the Yinping march and has him descend the cliffs wrapped in felt, the soldiers climbing. The stammer is a joke, and also his embarrassment when he meets Zhong Hui.
After Chengdu surrenders, the book has Zhong Hui and Jiang Wei plot to remove him. He dies shouting that he is wronged. The march is military history. The stammer is only how he spoke.
Reference: Wikipedia · Deng Ai