Yang Su
By 600, Emperor Wen's crown prince Yang Yong had lost the favor of Emperor Wen and Empress Dugu, over his wastefulness (which displeased Emperor Wen) and having many concubines (which displeased Empress Dugu). Yang Guang, whom Emperor Wen and Empress Dugu, had for some time plotted to replace Yang Yong, sent his associate Yuwen Shu to persuade Yang Su's brother Yang Yuē that, as Yang Su did not have a good relationship with Yang Yong, that if Emperor Wen died, Yang Su and his brothers would soon be in danger under Yang Yong's rule. Rather, Yuwen suggested, Yang Su should form a pact with Yang Guang and try to have Yang Guang made crown prince. Yang Su agreed, and began to discuss with Empress Dugu in earnest the possibility of replacing Yang Yong with Yang Guang. Empress Dugu was pleased, and requested Yang Su to persuade Emperor Wen as well. By fall 600, Yang Guang had Yang Yong's associate Ji Wei (姬威) falsely accuse Yang Yong of plotting treason. Emperor Wen commissioned Yang Su to investigate, and Yang Su intentionally misinterpreted evidence and manufactured additional evidence, causing Emperor Wen to believe that Yang Yong was indeed plotting treason. Emperor Wen deposed Yang Yong and created Yang Guang crown prince instead.