The answer depends on exactly what you are asking! There is also debate among Bible scholars.
Genesis contains the oldest recorded history - the creation account, the garden, the flood, and the tower of Babel. Genesis, and the next 4 books of the Bible were written by Moses.
The other book that many consider the oldest is Job. Job is considered the oldest recorded text in the Bible, many believing it was written 400 years prior to Moses writing Genesis. Many believe Job lived before the patriarchs - Abraham, Isaac, and Jacob. The author of Job is unknown.
We will not include the full discussion on this blog but point to the rich historical context that is grounded in the Bible. The Bible, inspired by God, contains stories of real events and real people that we can learn and be inspired by.