黃袍加身

Etymology
The idiom comes from the event in 960 when military commander removed child emperor  from the throne and proclaimed himself a new emperor after being presented an imperial dragon robe by his subordinates.

After becoming emperor, Zhao, for fear that military figures might betray him like he betraying his emperor, invited them to a wine banquet and successfully persuaded them to retire. This happened in 961 and gave rise to another idiom,.

Idiom

 * 1) to stage a coup d'état; overthrow a government; take the throne
 * 2) to be crowned (as a monarch, ruler, winner, champion, etc.)