Gregory Samuel Ain (March 28, 1908 – January 9, 1988) was an American architect active in the mid-20th century. Working primarily in the Los Angeles area, Ain is best known for bringing elements of modern architecture to lower- and medium-cost housing. He addressed "the common architectural problems of common people". Esther McCoy said "Ain was an idealist who gave the better part of ten years to combatting outmoded planning and building codes, and hoary real estate practices."