Alvin Marsh is Beverly Marsh's father, and a supporting character in the 2017 film, It.
While Alvin is seemingly a caring father to Beverly, he is actually a very abusive man. He doesn't feel comfortable about his daughter hanging out with Bill Denbrough and his friends, Eddie, Richie, Stan, and Ben, as she is the only girl in the group.
He always tends to get very hands-on with her, as well. When he does so, he asks if she is still his daughter. Eventually, this causes Beverly to become fed up with him and turn on him.