Léon Laustin, sometimes adapted as Léon Rostain, is a wealthy Parisian landowner fiercely proud of his family's near 300-year heritage. This deep-seated pride fuels his rigid class consciousness and drives his strategy to preserve lineage through advantageous marriages for his children. As patriarch, he openly scorns lower social classes, including commoners and servants. He therefore insists his elder daughter Geneviève marry Captain Victor Langlois for political and social gain, violently rejecting her affection for the piano teacher Jules Francoeur due to Jules's common birth. Discovering Geneviève's relationship with Jules provokes Léon's wrath; he disowns her and casts her out.

Beneath this stern exterior lies concealed compassion. After Geneviève's departure, Léon secretly entrusts the family coachman, Gaston, with an envelope of money for her, revealing unresolved paternal care beneath his unyielding principles. His pride in his son Andréa, a French army captain, shatters irreparably when Andréa is revealed as the revolutionary Count Red. Andréa's actions indirectly cause Marie's death during a hostage crisis at the Laustin estate. Léon publicly renounces Andréa, declaring him no longer his son.

Léon's obsession with status stems from a profound dread of becoming an "Impoverished Patrician." This fear materializes as the family's wealth and reputation collapse during the Prussian invasion, compounded by Thiers's political betrayals. After Marie's death, Thiers falsely accuses the Laustins of harboring Count Red, triggering malicious slander that destroys their name, evidenced by a sparsely attended funeral. Léon perishes in the fire consuming his estate, choosing to remain with the fatally wounded Marie rather than escape. His life, defined by unwavering adherence to tradition and lineage, ends in tragedy.