In many ways, Walton’s story parallels that of Victor’s. He is an exploratory man by nature, on an expedition to the North Pole to make some kind of discovery. Unfortunately, his ship gets stuck in some ice and his men fear they will die. He is torn between discovery and caring for people, much in the same way Victor is. He also writes letters to his sister.
Walton is also lonely in the way Victor and the monster are lonely. He desires a companion above all else, a friend with whom he can talk. He feels that he does not fit into society; he does not have a place, just as the monster does not. His thrill at having Victor arrive on his boat exemplifies his desire for friendship, as does his tragic disappointment when Victor dies.
When his crew asks if they can return to England, he at first says no, but later says yes, after hearing Victor’s tale about the overwhelming consequences of pushing the bounds of exploration. He learns from Victor’s story, in other words. After Victor dies, he turns the ship back, trying not to make the same mistakes that Victor made in the obsession that ruined his life.
Walton’s the only guy that’s not a total jerk to the monster. This could just be because he is similarly lonely, or, in the hopeful-Pollyanna sense, it could be that he learned from listening to Victor’s tale. Maybe he has some sophisticated and compassionate understanding of the monster, having heard the story? Then again, maybe not.