Mark Greaney is an American novelist focusing on thriller. He is best known as Tom Clancy's collaborator on his final books during his lifetime, and for continuing the Jack Ryan character and the Tom Clancy universe following Clancy's death in 2013. He is also known for the Gray Man series of novels, which was produced by Netflix into a feature film.

John Patrick Ryan Sr. (Hon.) is a fictional character created by author Tom Clancy and featured in his Ryanverse novels, which have consistently topped the New York Times bestseller list over 30 years. Since Clancy's death in 2013, five other authors, Mark Greaney, Grant Blackwood, Mike Maden, Marc Cameron and Don Bentley, have continued writing new novels for the franchise and its other connecting series with the approval of the Clancy family estate.