Who is Lao Tzu? It is indeed a mystery for eternity, and the following is a "possibility" analysis.
This question should be divided into two parts to explain, one is who is Lao Tzu recognized by the world? Second, who was Lao Tzu who wrote the Tao Te Ching?

Don't get dizzy, and listen to me.
First of all, let's first talk about who is the so-called Lao Tzu in the world?
There are very few texts that record Lao Tzu in ancient books, and many records are contradictory and confusing.
Sima Qian's "Records of History" records that Lao Tzu was a native of Ku County, Chu.
Moreover, it is recorded that Laozi's seventh grandson was on an errand for Emperor Xiaowen of Han, so that Laozi was probably a person in the middle of the Warring States period.
During the Republic of China period, many famous scholars such as Liang Qichao and Feng Youlan believed that Lao Tzu was a much later warring states person than Confucius.
But Confucius was a student of Lao Tzu, which is clear and confirmable in many ancient books.
In addition, Ban Gu's "Geographical Chronicle" records that during the Spring and Autumn Period, Ku County did not belong to the Chu State, but belonged to the Chen State.
The Qing Dynasty scholar Gu Zuyu said in the "Minutes of Reading the History of Fang Public Opinion" that Ku County was not a county in the Spring and Autumn Period, and it became a county in the Han Dynasty, and at that time it was not called bitter, but called Xiang.
The Book of the Later Han Dynasty also shows that Chen Ku was known in the Spring and Autumn Period.
In addition, at that time, the State of Chu was for southern man, and Xiongqu, the king of Chu, himself said:
I'm barbarian also.
We put ourselves in the humanistic environment at that time, and it is probably unrealistic for such a barbarian tribal land to give birth to such a great wisdom as Lao Tzu.
Based on the above, Sima Qianzhi's theory is difficult to stand.
Let's look again, Zhuangzi said that Lao Tzu lived in Peidi.
Yao Nai, a famous scholar of the Qing Dynasty, said after passing the examination that Lao Tzu lived in Peidi, Pei was located in the Song Kingdom, and the Song State had the surname of Lao.
This Song state was a fiefdom formed by the remnants of Yin Shang after Zhou defeated Yin Shang.
The Book of Zhou says:
But the Yin ancestors had books and books.
That is to say, in that era, only Yin Shang was a civilized person, with writing and books. Elsewhere are barbarian uncivilized tribes.
From this point of view, it is very likely that such a great wisdom as Lao Tzu is the remnant of Yin Shang.
Lao Tzu was a historical official of the Zhou Dynasty, which was hereditary at that time, which means that the Laozi family has been a historical official for generations.
The book of Zhuangzi describes lao tzu's death:
The old man died, Qin You hung up, and the third number came out.
Here it is roughly illustrated that Lao Tzu died in Qin, that is, in Shaanxi.
In addition, we also know that Lao Tzu disappeared through Hangu Pass in his old age. Hangu Pass is right in the middle of Fenghao (Xi'an Generation) in Shaanxi and Luoyi (Luoyang) in Henan.
According to the above information, we can analyze and know that the Laozi family was in Fenghao, Shaanxi in the early days, And Laozi later moved east with the Zhou Dynasty to Luoyi, Henan, returned to Shaanxi through HanguGuan in his old age, and finally died in Shaanxi, so the coincidence was very high.
This Lao Tzu is known to the world as Lao Tzu, but not necessarily the Lao Tzu who wrote the Tao Te Ching.
Why not necessarily Lao Tzu who wrote the Tao Te Ching?
First of all, the Tao Te Ching is not the original of Lao Tzu's book, it is only a popular version of Lao Tzu's book, and it is an annotated version of future generations.
Among them, the three characters of the Tao Te Ching were also drafted by the Heshang Gong of the Western Han Dynasty.
The Laozi Book excavated from the Mawangdui Han Tomb in Changsha is older than the Tao Te Ching, but it is not necessarily the original of the LaoZi Book.
So we call this original book Lao Tzu for the time being.
So why wasn't the book of Lao Tzu written by Lao Tzu, as the world knows?
Sima Qian's "Records of History" records:
At the end of the pass, Guan Ling Yin Xi said: "The son will be hidden, and he will write a book for me." So Lao Tzu wrote the first and second chapters of the book, saying more than five thousand words of morality, and did not know the end.
This account is very suspicious (from the very low level of civilization conjecture at that time):
1. When we look at the Tao Te Ching (this text is seen by the world, the book of Lao Tzu), the depth, breadth, and completeness of its thinking are not something that a person can write under the circumstances of the emergency at that time.
2. At that time, the book was written with Jian Mu, and its production process was quite cumbersome, how could there be so many Jian Mu used to write more than 5,000 words in one level?
At that time, scholars generally did not write books, and preached through the form of apprentices, such as Confucius.
Because the Lao Tzu family was a hereditary historian at that time, the possibility of writing books was very large.
In summary, the book of Lao Tzu was not written by The world as known as Lao Tzu as mentioned above, but is likely to be jointly written by a family of Lao Tzu.
The Lao Tzu known to the world is recognized by the world because it brought famous students such as Confucius, Wenzi, Yang Zhu, juanzi, etc., as well as related famous allusions, and can be regarded as a representative of the Lao Tzu family.
Final summary:
1. The world believes that Lao Tzu, whose family was a remnant of yin merchants, hereditary historians, was initially in Fenghao, Shaanxi, Laozi later moved east with the Zhou Dynasty to Luoyi, Henan, and returned to Shaanxi through Hanguguan in his old age (after the rebellion of the prince's dynasty), and finally died in Shaanxi.
2. Lao Tzu, who wrote the Book of Lao Tzu, is not one person, but many people in the Lao Tzu family.
There are many relevant evidences above, which are the research of university people, not my work.