Daode Tianzun (道德天尊) is the official title for Tàiqīng (太清): the Grand Pure One, which is one of the Three Pure Ones. He is commonly known as Taishang Laojun (太上老君) "The Grand Supreme Elderly Lord". His other names include Daode Zhizun 道德至尊 "The Universally Honoured Virtuous One", Daojiao Zhizu (道教之祖), the Taoist Ancestor. Laozi is regarded to be a manifestation of Daode Tianzun who authored the classic Tao Te Ching.
His manifestation anniversary falls on the 15th day of 2nd month of the Chinese lunar calendar.
References
Daode Tianzun Wikipedia(Text) CC BY-SA