Vaillant complements the cold reserve of Latour. Whereas Latour is handsome, calculated, and emotionally distant, Vaillant is homely, impulsive, and sometimes too vehement. Despite these qualities, Vaillant required Latour's support in order to find the strength to leave France for the New World.
He loves good food and drink but is able to convert this into vigorous spiritual energy. He applies his energy and boundless enthusiasm to the Church, frequently begging for monies to benefit his churches and even charming Manuel Lujon out of his two cream-colored mules.
His motto is "Rest in action." Impulsive, he throws his arms around Manuel Lujon, hops on his mule like a grasshopper, and cries over the separation from Latour. His ease in making friendships allows him opportunities to enter difficult situations where there is prejudice against the new regime and dissolve all ill feeling as he does when he prepares the people of Santa Fe for the return of their new bishop.
Possessing a weak physical constitution since childhood, Vaillant is often sick and suffers such physical injuries as broken bones during his missionary travels. Although he cares little for art or architecture, he loves music and enjoys singing.
Unlike Latour, he believes only in miracles that occur outside of natural laws. His enthusiasm endears him to many, including Father Revardy and the Pope. He overextends the finances of his diocese in Denver, prompting a command to visit the Vatican in order to explain himself.
Vaillant is close to his family. He writes often to his sister, Philomene, a Mother Superior in a French convent.