A biographer is a writer who specializes in true stories of other people's lives. The finished books that biographers publish are called biographies.
In some cases, well-known writers, actors, and other public figures work with biographers in order to collaborate on their own biographies. Other times, biographers research the lives of their subjects after they've died. In the 1660s, they were known as biographists. The root of all variations on biography is the Late Greek biographia, "description of life," from bio-, "life," and graphia, "record or account."