The primary scripture of Taoism is the "Tao Te Ching," which is also sometimes called the "Laozi" after its purported author, Lao Tzu. However, Taoists also venerate many other works, including the "Zhuangzi" and the "Liezi," authored by Chuang Tzu and Lieh Tzu respectively. The term "tzu," or "zi," roughly translates to "master."
According to legend, Lao Tzu was traveling out of China in the sixth century B.C. when a guard at the Great Wall asked him to relay his wisdom for the ages. Master Lao dictated the entirety of the "Tao Te Ching" to this guard, and it was passed down through history. Most modern Taoist scholars believe Lao Tzu was an invented character, and the book simply represents a collection of the wisdom of the earliest Taoist sages.
While the "Tao Te Ching" is considered Taoist scripture, it is not venerated to the extent that holy books in Western religions are. The book opens with an admonition that "the Tao that can be spoken is not the eternal Tao," meaning that the wisdom described in the book is only a pale shadow of the true path. The text is filled with duality and paradox, and the classical Chinese in which the original text is written is notoriously difficult to translate. With no punctuation marks, the meanings of specific passages can be altered by the translator, leading to many different versions of the text.