裴寂 / Pei Ji
裴寂 / Pei Ji enters the wiki through Qinji 131-2 as the banquet organizer in the Jinyang-palace story. The source says he repeatedly urges 李渊 to drink and then uses the resulting exposure to argue that rebellion is now safer than waiting for punishment.
His function in the episode is tactical. Pei Ji turns alcohol, sex, palace space, and the authority of 杨广 into a no-return situation, while 李世民 belongs to the same persuasion setup.