Who was Jasher, the author of a book referenced in the bible?

Who was Jasher?

The scripture in question is:

"And the sun stood still, and the moon stayed, until the people had avenged themselves upon their enemies. Is not this written in the book of Jasher? So the sun stood still in the midst of heaven, and hasted not to go down about a whole day."-Joshua 10:13 (NWT) [italics mine]

According to the Benson Commentary:

It was probably a collection of records, or of poems, concerning the principal events of these wars, and no doubt gave a further account of this miracle. But this and some other books of these ages have long been lost, not being canonical, and therefore not preserved by the Jews with the same care wherewith they guarded their inspired writings.

Within the Scriptures, there are other references to books or scrolls that are not part of the Bible canon.

A "Questions From Readers" published in the Watchtower March 15, 2009 gives some additional information.

Nobody knows who the original author of the Book of Jasher was, although it is mentioned in Joshua 10:12-13 and in 2 Samuel 1:18-27. Neither has the original manuscript survived.

What we do know is that it was also known as the “Book of the Upright One” in the Greek Septuagint and the “Book of the Just Ones” in the Latin Vulgate. The Book of Jasher was probably a collection or compilation of ancient Hebrew songs and poems praising the heroes of Israel and their exploits in battle. The Book of Jasher is mentioned in Joshua 10:12-13 when the Lord stopped the sun in the middle of the day during the battle of Beth Horon. It is also mentioned in 2 Samuel 1:18-27 as containing the Song or Lament of the Bow, that mournful funeral song which David composed at the time of the death of Saul and Jonathan.

There is a book called “The Book of Jasher” today, although it is not the same book as mentioned in the Old Testament. It is an eighteenth-century forgery that alleges to be a translation of the “lost” Book of Jasher by Alcuin, an eighth-century English scholar. There is also a more recent book titled “The Book of Jashar” by science fiction and fantasy writer Benjamin Rosenbaum. This book is a complete work of fiction.

Another book by this same name, called by many “Pseudo-Jasher,” while written in Hebrew, is also not the “Book of Jasher” mentioned in Scripture. It is a book of Jewish legends from the creation to the conquest of Canaan under Joshua, but scholars hold that it did not exist before A.D. 1625. In addition, there are several other theological works by Jewish rabbis and scholars called “Sefer ha Yashar,” but none of these claim to be the original Book of Jasher.

Here is an extract from a Wikipedia article on the Sefer haYashar, or the Book of the Upright:

Sefer haYashar (ספר הישר) is a medieval Hebrew midrash, also known as the Toledot Adam and Divrei haYamim heArukh. The Hebrew title "Sefer haYashar" might be translated as the "Book of the Correct Record" - but it is known in English translation mostly as The Book of Jasher following English tradition. Its author is unknown.

The book is named after the Book of Jasher mentioned in Joshua and 2 Samuel. Although it is presented as the original "Book of Jasher" in translations such as that of Moses Samuel (1840), it is not accepted as such in rabbinical Judaism, nor does the original Hebrew text make such a claim. It should not be confused with the very different Book of Jasher (Pseudo-Jasher) printed by Jacob Ilive in 1751, which was purported to have been translated by the English monk Alcuin. It should also not be confused with an ethical text by the same name, which, according to the Encyclopaedia Judaica, Volume 14, p. 1099, was "probably written in the 13th century."

The Bible twice quotes from a Sefer haYashar, and this midrashic work includes text that fits both Biblical references - the reference about the Sun and Moon found in Joshua, and also the reference in 2 Samuel (in the Hebrew but not in the Septuagint) to teaching the Sons of Judah to fight with the bow. This appears in Jasher 56:9 among the last words of Jacob to his son Judah: Only teach thy sons the bow and all weapons of war, in order that they may fight the battles of their brother who will rule over his enemies. (MCR)

But the book as a whole was written much later - as shown by chapter 10, covering the descendants of Noah, but containing medieval names for territories and countries, most obviously Franza for France and Lumbardi in Italia for Lombardy. The text of this chapter closely follows the beginning of Josippon, a tenth-century rabbinic text that lists the various peoples living in Europe in ca. 950. Source: Sefer haYashar (midrash)

Based on the Hebrew used and other indicators, it seems that this work was written in Naples in the early 16th century, probably by a Jew who lived in Spain or southern Italy. Nothing is known of the man who wrote the original book of Jasher, possibly some 4,000 years ago.