I would argue the woman who dies in the fire, Clarisse and Beatty are all people who move Montag to change.
The woman at the beginning of the book chooses to burn with her books rather than leave her home and her books behind. She lights the match herself and goes up in flames. This event in Montag's life changes him. In Montag's life, he feels no passion for anything or anyone that would cause him to give up his life for. Montag decides that if she is willing to die for books, there must be something important, powerful and wonderful within the covers of a book.
Clarisse talks to Montag the first day they meet about nature, details of life, talking, relationships and the purposeless way that people her age lead their lives. The poignant changing moment though is when she asks Montag the first day they meet "are you happy?" This question confuses Montag, and makes him ponder his life's purpose for days and weeks to come. This, coupled with Mildred's attempted suicide, makes him realize that people in their society are not happy at all. There is something missing.
Beatty quotes literature and philosophy to Montag trying to confuse him and expose the contradictory comments that books make. He shows Montag that there is pain and horrors in history and literature, and he almost succeeds in confusing Montag into submission. However, with the help of Faber, Montag realizes he is sick of being manipulated into how to think and feel. With Beatty standing in front of him, he makes the most active decision and kills Beatty with a flame thrower. This active killing shows that Montag has been transformed by these important people in his life.