Introduction
Daodejing and the Zhuangzi are the most representative texts of the seminal phase of Daoism, called by scholars "Proto-Daoism" or “Classical Daoism”. These early texts and their related communities formed the foundation for a organized Daoist religious tradition, which became formally established during the Later Han dynasty (220-589).  But these must not be considered as the only authoritative texts of Daoism. In fact, in the 5th century  started the first compilation of the Daoist Canon, which now comprise more than 1400 texts, with commentaries, ritual prescription, enchantments, and so on.

Pivotal events for the Tradition: "Classical Daoism" developments
In China the Period of Warring States (480-222 BCE) signed the decline of the Zhou dynasty (1050-256 BCE). It was a time of immense political strife, violent social upheaval that triggered an intellectual debate (whose participants would have been subsequently categorized as " One hundred school of thoughts") about what was the best way - the best Dao -  to be chosen to overcome such a difficult period. Among them there was the so-called “Daoist school”, but scholars tend to describe it as a numbers of loosenly associated master-disciple communities that emphasized mystical unification with a sacralized Dao through quietistic meditation. This period in Daoism is usually called “Classical Daoism”or "Proto-Daoism".

Sacred texts and other main texts: the Daodejing
The Daodejing is largely an anthology of earlier sayings and teachings. It consists of textual layers from a variety historical periods. From a literary point of view, the Daodejing is distinguished for its highly compressed style. Unlike the composition of other contemporary treatises, it articulates its cryptic subject matter in short, concise statements. It has been open to many interpretations: various readings concerning self-cultivation, ruling the state, physiological or alchemical interpretations and so on. The Daodejing moreover has been used as a sacred text that, like all sacred writings, must be recited in conjunction with meditation and ritual practices for exorcism and healing purposes.

Sacred texts and other main texts: the Zhuangzi
The Zhuangzi provided Daoism with doctrines, notions, and technical vocabulary throughout its history. It is masterpieces of Chinese literature as a whole and differs from the Daodejing from the point of view of its formal features, largely consisting of stories, anecdotes, and reflections. Zhuangzi himself probably authored the seven so-called Inner Chapters in the late 4th century BCE, with the other portions dating from one or two centuries later.

Deities and other holy Beings: Laozi
Laozi is the pseudo-historical figure of the author of the Daodejing, whose official biography dates around 150 BCE. Some scholar contends that if Laozi existed, we do not know anything about him. Sometimes he has been considered the founder of Daoism, but in fact he is not. He was just the revered figure of the sage who expounded the doctrines of the Daodejing. Moreover, In the second half of the 2nd century CE, at the beginning of the formation of the first major Daoist religious movement there was the deification of Laozi as a messiah who embodies the Dao and reappears at different times either as a sage counselor of political rulers or as the inspirer of religious leaders.

Source Analysis
Source n° 1
Excerpts from the Daodejing
Chapter n° 1 explains how the inner reality of the Dao, which is the source of everything, is ultimately beyond human language and rational comprehension, because it represents primordial undifferentiation or pure potentiality. It can be described only in its phases of differentiation — all of which occur simultaneously. In fact In chapter n° 42  is described how from the Dao proceeds the One, that is, the Primordial Qi , which in turn divides in two, that is, Yin and Yang Principles. At this moment Yin and Yang have not yet formed patterns of interaction. In fact, their interaction is referred to as “three;” which is a moment that involves Yin and Yang in dynamic and continual interaction, resulting in further differentiation. This further differentiation leads to the emergence of all existing things and beings, in which the Dao is immanent.
Given the continuous interaction of Yin and Yang, all parts of the universe are subjected to periodical mutations and are relative to each other, as chapter 2 explains. Therefore, is useless to force the pattern of the cosmos as one desires. The wise man doesn't act towards the world, trying to hold its change. This important concept of Classical Daoism is called Wu Wei (not-doing) and its epitomized in chapter 64. This ideals of Wu Wei is not limited only to the individual: also society should abandon its laws, technology and knowledge. The sage ruler employs the Wu Wei  principle and lets that the people attune naturally with the Dao, as chapter 57 explains.
Wu Wei is not an ideal of absolute inaction nor a mere "not-overdoing." It is an action so well in accordance with the way of the things that its author leaves no trace of himself in his work. There is no true achievement without Wu Wei  because every deliberate intervention in the natural course of things will sooner or later turn into the opposite of what was intended and will result in failure.

Source n° 2
Excerpts from the Zhuangi
The Zhuangi provided Daoism, among others, with the religious ideal of the Perfect Man. Chapter one give us a poetic and fantastic depiction of this ideal. The Perfect Man has identified his life rhythm so completely with the rhythm of the forces of nature (that is, the Dao) that he has become indistinguishable from them and shares their immortality and infinity.  From a more existential point of view, the mystic realization of the unity with the Dao blurs the distinction between the self and the world. This idea also governs Zhuangi's attitude toward death. Life and death are but one of the pairs of cyclical phases, such as day and night. In the case of Zhuangzi's wife, she first is part of the undifferentiated Dao, then a change occurs and she is part of the  Primordial Qi, then she is a body, then she is born, and finally, after an another change, she is dead.

Source n° 3
Laozi Riding and Ox
According to the legend of Laozi as the author of the Daodejing, when he perceived that his land was in decline, departed. It is said that when he went through a valley pass, the official Pass Commissioner Yin Xi felt the presence of a purple mist suddenly appearing in the air. He presumed that a great sage was passing through the area. Not long thereafter appeared Laozi riding on his blue ox from the east. Yin xi implored Laozi to write down a book for later generations. Laozi consented and lend to the Official Pass the famous Daodejing. Then, he got on his ox and rode off to the west, never to be heard from again.

Intercultural, interdisciplinary information
The Daode jing, in its various  “translations” and adaptations for the scholars' community but also for the general public, has also become part of popular Western culture as one of the most known East Asian text.
However, it is often translated and read as part of some universal wisdom tradition, alternative spirituality.
This approach to this and other Daoist texts can be traced back to The German philosopher Leibniz ( 1646-1716s), who was among the first of the European intelligensia to see in the Chinese classics and Daoist thought, a true religious expression of philosophia perennis, the ancient and perennial, unitary truth underlying all great religions. By the late 19th century, “Classical Daoism” was constructed, in an orientalist paradigm, as a text-based philosophy, a perennial wisdom tradition that “reflected a timeless spiritual quality” while “later” or “religious” Daoism was seen as a decline from its original essential purity.
The philosopher Martin Heidegger, for example, seems to have drawn on German translations of the the Daodejing  as primary sources  for his philosophical reflections after writing "Being and Time".
For more information: http://www.esoteric.msu.edu/VolumeVI/Dao.htm