Dr. Mario Mercado left Puerto Rico at the age of 17, recently graduated from high school, determined to become a veterinarian. In Iowa, United States, he attended university and worked as a teacher; then, he enlisted in the military, worked with the federal government in the state of Florida and, when he was already thinking about retirement, he accepted to return to the island to be part of the faculty of the first Puerto Rican school of veterinary medicine.