Steve Kloves is the guy who wrote the scripts for all the Harry Potter films except for Order of the Phoenix. He bowed out for Phoenix to write the screenplay for a movie version of The Curious Incident of the Dog in the Night-Time, a project which ended up in Development Hell anyway. Prior to his work on the Potter series, he wrote and directed The Fabulous Baker Boys, which coincidentally is one of J. K. Rowling's favorite films. He's also a co-writer for The Amazing Spider-Man.
Throughout the ten years he worked on the Potter series, Kloves had to consult Rowling for information about which details would come to play in future installments. She refused to tell him how the series would end, but she still told him more than anyone else, "which I probably shouldn't say on screen, or they'll kidnap and torture him." Kloves and Rowling developed a friendly working relationship and both have spoken highly of each other.