Martín Casillas (1556–1618) was a Spanish architect, best known for designing the Cathedral of Guadalajara in Jalisco, Mexico. In recognition of his work, Casillas was rewarded with land in the highlands of Jalisco, which was passed down through his family for many generations.
Casillas's living descendants include brothers Mario Casillas Rabago and Gregorio Casal (born Jose de Jesus Casillas Rabago), both well-known film actors in Mexico. They are the sons of Jose Casillas Lozano and Carmen Rabago, who both hail from San Miguel El Alto Jalisco, where Don Martín's original Jalisco estate was located. Also, Art Martinez de Vara Mayor of Von Ormy, Texas.
Several people with the surname Casillas have submitted DNA results. The descendants with a well documented paper trail back to Martín Casillas belong to the R1b-152 haplogroup.