The Heibai Wuchang, or Hak Bak Mo Seong, literally "Black and White Impermanence", are two deities in Chinese folk religion in charge of escorting the spirits of the dead to the underworld. As their names suggest, they are dressed in black and white respectively. They are subordinates of Yanluo Wang, the Supreme Judge of the Underworld in Chinese mythology, alongside the Ox-Headed and Horse-Faced Hell Guards. They are worshiped as fortune deities and are also worshiped in City God Temples in some countries.
In some instances, the Heibai Wuchang are represented as a single being – instead of two separate beings – known as the Wuchang Gui, literally "Ghost of Impermanence". Depending on the person it encounters, the Wuchang Gui can appear as either a fortune deity who rewards the person for doing good deeds or a malevolent deity who punishes the person for committing evil.
