Final answer:
Laozi appeared to Zhang Daoling in a vision, according to Daoist tradition, and authorized him to establish a system of beliefs and practices within Daoism, granting him the title of Celestial Master.
Step-by-step explanation:
The individual who appeared to Zhang Daoling and gave him authority to create beliefs and rituals based on Daoism was Laozi. According to Chinese tradition and Daoist beliefs, Zhang Daoling, a fangshi magician, had a vision during which Lord Lao, also known as Laozi, appointed him as Celestial Master. Lord Lao bestowed upon Zhang Daoling healing powers and instructed him to gather followers to prepare for the end of the world, teaching them to purify themselves for a new epoch.
Historical sources describe Laozi as the founder of philosophical Daoism, who is traditionally credited with writing the Daodejing (Tao Te Ching), although the historical existence of Laozi is a topic of scholarly debate. Nonetheless, the teachings attributed to Laozi have greatly influenced the development and practices of Daoism, and Laozi is revered as a deity in religious Daoism, reflected in Zhang's vision granting him the status of Celestial Master.