Gerardo Murillo (October 3, 1875 – August 15, 1964) was a Mexican painter and writer who signed his works "Dr. Atl". He was born in Guadalajara, Jalisco, where he began the study of painting at an early age, under Felipe Castro. At the age of 21, Murillo entered the Academy of San Carlos in Mexico City to further his studies.

After showing his abilities, Murillo was granted a pension by President Porfirio Díaz to study painting in Europe. There he broadened his scope of learning, with study of philosophy and law at the University of Rome, and many trips to Paris to listen to lectures about art given by Henri Bergson. His strong interest in politics led him to collaborate with the Socialist Party in Italy and work in the Avanti newspaper. It was at this time that he was baptized "Dr. Atl" (the Nahuatl word for "water") by Leopoldo Lugones.