Who is the author of Old Testament book psalms?

The book of Psalms credits King David as authoring about half of the book of Psalms, other authors credited in the book are Moses, Solomon, Herman, Ethan, the sons of Korah, and the sons of Asaph.

About a third of the psalms have no author's name prefixed to them.

They all were complied together in to the book of Psalm by an unknown priest or rabbi at a later time.