Hēidì (Chinese: 黑帝; lit. 'Black Deity') or Hēishén (黑神; 'Black God'), who is the Běidì (北帝; 'North Deity', Cantonese: Pak Tai) or Běiyuèdàdì (北岳大帝; 'Great Deity of the Northern Peak'), is a deity in Chinese religion, one of the cosmological "Five Forms of the Highest Deity" (五方上帝; Wǔfāng Shàngdì). He is also identified as Zhuānxū (颛顼), today frequently worshipped as Xuánwǔ (玄武; 'Dark Warrior') or Zhēnwǔ (真武), and is associated with the essence of water and winter. His animal form is the Black Dragon and his stellar animal is the tortoise-snake. By virtue of his association with the north, he has been identified and revered frequently as a representation of the supreme God of Heaven.

His planet is Mercury. His animal form is the Black Dragon and his stellar animal is the tortoise-snake.

A Taoist title of Heidi is the "Dark (or Mysterious) Heavenly Highest Deity" (玄天上帝; Xuántiān Shàngdì). According to a myth, during the fall of the Shang, the Demon King ravaged the world, so that Yuanshi Tianzun ordered the Jade Emperor to appoint Heidi as the commander of twelve heavenly legions to fight this evil. Heidi defeated the Demon King and was subsequently granted the title of Mysterious Heavenly Highest Deity. In temples dedicated to him, the bronze tortoise and serpent under the feet of his image signify that the good always prevails over evil.

In Hong Kong, it is worshipped among other places in:

Note : A territory-wide grade reassessment of historic buildings is ongoing. The grades listed in the table are based on these updates [1] [2] (8 June 2023). The temples with a "Not listed" status in the table below are not graded and do not appear in the list of historic buildings considered for grading.