Montag is the main hero in Fahrenheit 451. He becomes driven by a hunger for knowledge, but to pursue this he must accept that he'd been brainwashed for his entire life up to that point. He doesn't only want to awaken himself; he tries to get Millie to accept that they have lived lives of mental suppression but she is unwilling to do so.
At the end of the novel, he is forced to kill Beatty and the two other firemen. He flees for the river after this but he was already an enemy of the State. By pursuing literature and free speech, Montag loses his wife, his job, and potentially his life. In spite of all this, he doesn't relent.
Montag had been under the illusion that he was happy. Clarisse was the first to (indirectly) point this out. However, it was a comfortable illusion. In order to be mentally free, Montag had to alienate himself, remove himself from this life and in doing so, he had to destroy it. Montag had to be brave enough to become like the Phoenix.