Who is Margaillan from The Masterpiece and what is their importance?

Margaillan is proof that the common man can become a great man with hard work and clever business dealings. Over time, he became one of the foremost builders in Paris. He personally chooses Dubuche as his daughter's husband, believing that he will be an asset to his business. When Dubuche fails as an architect, he sends his son-in-law to the country to care for his wife and frail children.