"The Fountain" also stars Ellen Burstyn as Dr. Lillian Guzetti, Tom's superior, and Mark Margolis as Father Avila, who accompanies Tomás the conquistador. Burstyn and Margolis appeared in Aronofsky's "Requiem for a Dream", and the director wrote into the script roles for both of them. Sean Patrick Thomas, Donna Murphy, and Ethan Suplee were cast as assistants to Tom's lab work. Cliff Curtis was cast as Captain Ariel, a fellow conquistador, and Stephen McHattie was cast as Grand Inquisitor Silecio, a religious fanatic who threatens the Spanish queen. Seventy extras were cast as Maya warriors, including twenty who had actual Guatemala Mayan backgrounds. One of the twenty, a real-life spiritual leader, was cast as the Maya spiritual leader in the film.