Guillermo is the Spanish form of William, a Germanic name made of wil, "will", and helm, "helmet", so it means "resolute protector". Film director Guillermo del Toro, winner of the Academy Award for The Shape of Water, is the name's most prominent bearer in the United States today. Guillermo ranked number 392 in 2000 and has slipped steadily since, to number 661 in 2015 and number 902 in 2025.