As the old saying goes, the truth is often more complex, and beyond imagination. The facts we known are there are physical evidence that at least 3 century BC, a book collection containing 3 parts of Laozi (started from modern chapter 18), with some lost pieces of chapters existed. The lost chapters are hard to recognized since no reference to compare to, and the part that do recognized is largely due to a later version, that has similar chapter structure (which Te Ching is in front and Tao Ching in the back) about 100 years later is discovered as well. And the sentences / chapters in those 2 oldest known version, are not complete. 2000+ years underground in a tomb with writing on wood are not that well preserved. But the sentences do complete, is almost identical to the one we saw in later version (there are different versions recorded when and by whom they altered from that till today's version), except some words difference, possibly do to human error, or the sound of some words changes over time. And some are meaningful changes but replaceable, due to the words are no longer used in later time, some concept are archaic, and need to be rewrite in later era.
And the "books" are not that easy to copy or print like today, people use knife to carve writing on wooden sticks, and link them with threads. So writing errors are common, more importantly many books are first made public by people who memorizing it and reciting to others (the reason why the books are name after its author at that time, since every sentence will begin as "Someone said", like the famous "Confusions said"). Not many people can read. Also, since the nations at that time are using basically different languages, possibly as far apart as English and French. So someone needed to translate the words before he can recite to other people from different nations. (The written characters may look alike from nation to nation, but the pronounces and usage of oral phrases will be very different. And its very well documented as people can easily tell each other apart by what they speak).
So it increase the difficulty of determine the source. Since it can very well started as 1 author and 1 version, and told to others by verbal, and translated again and again. Someone may add their opinions in it. And this process goes on probably till the beginning of War Nations about 100+ years later. (when more books started to be preserved physically). However the style the words it used and its grammar is a clue to us, that its very old, since it use some words no longer used in later period, it has structure that no longer existed, and the use of words are more down to verbal phrases than official writing phrases. Although all the above may point out that there are multi-authors, however its consistence using same semantic phrases, also the contemporary books has mentioned Laozi many times. And the record about who he is as we know, are recorded with in those books. But those books themselves are suffer the same problems as Laozi. So not very concrete evidences. And the lost chapters indicate also either later editors (librarians) deliberately delete them, or they are lost in history during the massive wars unifying China. And later Taoism mystified the books and Laozi didn't help either.
And from records of other books, it all said Laozi is just (as previous poster says) a honorable title (Old gentleman is probably a better translate, Lao is old, Zi is a general title for man like Mr. today). His name is Lee Er 李耳(or Dan 聃), the description about long ear is probably added later, due to the word's meaning in later time, but remember the pronounce of words are very different from nation to nation, its never possible to tell what it sounds like 2500+ years ago. So some one do name Lee Er (or close, the writing is different as I mentioned in older post) probably existed, related to the books called Laozi. Whether he is Laozi the title holder, of the title isn't meant for him only is unknown. Its made from many authors is probably true (told by many using verbal words and adding their words as well), but whether they really composed major part of the books, and no central authors, probably NOT true. The core of the books are backup by physical evidences. And those words are very likely comes from someone with the honor title of Laozi. And its a very different looking books from today's version.