Records of the Three Kingdoms
Yang Yi, courtesy name Weigong, was from Xiangyang. He served as a clerk under Guan Yu, later joined Liu Bei, and became Zhuge Liang’s chief clerk. On the northern campaigns he planned movements and grain. Zhuge Liang often only had to glance at the work. He and Wei Yan hated each other. Zhuge Liang’s authority kept both men in one army.
In 234 Zhuge Liang died of illness at Wuzhang. The death was kept secret, and Yang Yi was to manage the retreat. Wei Yan would not take orders from him. He led his own troops south first and burned the gallery roads. Supported by Fei Yi and others, Yang Yi declared Wei Yan a rebel. Ma Dai killed Wei Yan. Back in Chengdu the regency went to Jiang Wan, not to Yang Yi. Yang Yi thought his years and rank were senior. He said aloud that if he had taken the army over to Wei he would not have come to this. In 235 he was stripped of office, sent to Hanjia, and killed himself there.
Romance of the Three Kingdoms
The novel makes Wei Yan’s death a sealed instruction Zhuge Liang left in life. Yang Yi, following it, lures Wei Yan into shouting “who dares kill me,” and Ma Dai cuts him down from behind. The bone of rebellion is the novel’s verdict, planted in advance.
Yang Yi’s disappointment, his complaint, and his suicide remain. The sealed order turns a feud between colleagues into something the chancellor had already scheduled.
Reference: Wikipedia · Yang Yi