Dylan McDermott's original name was Mark Anthony McDermott. He changed his name after his father's 3rd wife's miscarriage; the miscarriage baby's name was supposed to be Dylan. McDermott was very close to his father's 3rd wife, and she was the one who inspired and motivated him to act.
You probably know him best from his roles as Bobby Donnell in The Practice and Lt. Carter Shaw in Dark Blue, although he has played many other parts also. You might have also seen Dylan in the movies Twister, Steel Magnolias, Hardware, Miracle on 34th Street, Texas Rangers, Party Monster, Wonderland, Runaway Jury, The Messengers, Burning Palms, and The Perks of Being a Wallflower.
McDermott has also made appearances on the shows Tales from the Crypt, Will & Grace, Big Shots, and is currently a main character on FX's American Horror Story.