Final answer:
Traditionally, Moses is credited with authoring the most books of the Old Testament, referred to as the Torah or Pentateuch, which includes the first five books. However, modern biblical scholarship recognizes multiple authors and sources in its composition.
Step-by-step explanation:
The question of which author contributed the most books to the Old Testament is somewhat complex due to the multiple authors and redactors involved in its composition over many centuries. However, traditionally, Moses is credited with the authorship of the first five books of the Old Testament, known as the Torah or Pentateuch. It's important to note that modern scholarship discusses the documentary hypothesis which suggests that the Torah was compiled from several sources by multiple authors.