The Laozi of philosophy is only half the figure. In religious Daoism he was raised to a god, and the history of that elevation is a subject in its own right.
By the second century CE the movement of the Celestial Masters, conventionally dated to a revelation received by Zhang Daoling in 142, venerated a deified Laozi as Taishang Laojun, the Most High Lord Lao, a cosmic deity who periodically descends to teach humanity and who came in time to be numbered among the Three Pure Ones at the summit of the Daoist pantheon. The philosopher of the mountain pass had become an eternal manifestation of the Dao itself; Livia Kohn's study traces how the man, the book and the god were woven together over the centuries.
Two episodes show how far the myth could be pressed. The old story that Laozi rode west through the pass was extended into the claim, the huahu, "conversion of the barbarians", that he continued into India and there became, or taught, the Buddha. Advanced in the rivalry between Daoists and Buddhists, the Huahujing that set it out was repeatedly attacked and, under the Mongol Yuan, ordered destroyed. And in the Tang dynasty the imperial house, which shared Laozi's surname Li, claimed him as its ancestor and honoured him with grand titles, binding the deified sage to the legitimacy of the state.
The distance between this cosmic Lord Lao and the elusive archivist of the earliest accounts is a measure of what a tradition can build on a figure whose very existence its first biographer could not confirm.