This character doesn’t have a role at all. His personage isn’t dynamic; he appears not so often. So, what do we definitely know about him? He is Emma’s father; he is very simple, kind and calm farmer. He is completely devoted to his daughter and to the memory of his first wife whom he loved so much that after her death he couldn’t handle with himself at all. That is why it is obvious that the next thing which happened to him was his weakness to drink more and more. He did it because he wanted to forget about his pain, about a passed wife.
What can we say after such short information about him given in a book? That probably he was also the reason for Emma’s desires to have the better family full of love. She saw that love in her own family is a child and wanted to copy it. Unfortunately, her mother’s death ruined the happy life of Emma and Monsieur Rouault.
But it is only a suggestion; maybe Emma spilled her life for her own reasons, without having such a background on her mind.
Monsieur Rouault in the Essays