Ralph Ward Stackpole (May 1, 1885 – December 10, 1973) was an American sculptor, painter, muralist, etcher and art educator, San Francisco's leading artist during the 1920s and 1930s. Stackpole was involved in the art and causes of social realism, especially during the Great Depression, when he was part of the Public Works of Art Project, Federal Art Project of the Works Progress Administration, and the Treasury Department's Section of Painting and Sculpture. Stackpole was responsible for recommending that architect Timothy L. Pflueger bring Mexican muralist Diego Rivera to San Francisco to work on the San Francisco Stock Exchange and its attached office tower in 1930–31. His son Peter Stackpole became a well-known photojournalist.

Stackpole worked as a laborer early in life to support himself and his mother following the death of his father in a lumber mill circular saw accident. At sixteen, he came to San Francisco to study at the California School of Design (now San Francisco Art Institute) beginning in 1903; he was influenced strongly by Arthur Frank Mathews, muralist and painter at the school. He met painter Helen Arnstein (later Helen Salz) while both were teenagers, and she became his first girlfriend. Arnstein, the daughter of wealthy Jewish art lovers and one year Stackpole's senior, described him as "a remarkable draftsman" who painted and sketched constantly. She was less impressed with his sense of color than with his precision in line. Stackpole polished his craft by working with artists at the Montgomery Block, playfully called "Monkey Block", a bohemian hangout which included studios for painting and sculpture. After the 1906 San Francisco earthquake, he used a grant of US$200 ($7,200 in current value) to travel to France to attend the École des Beaux-Arts in the class of Antonin Mercié in 1906–1908, exhibiting at the Salon in 1910. It was in Paris that he became friends with painter Diego Rivera He painted under Robert Henri in New York in 1911.

Stackpole returned to San Francisco in 1912 and married Adele Barnes, two months younger than he, an art student of Xavier Martínez and one of the first graduates of the California Academy of Arts and Crafts. Adele Stackpole was a perfectionist in many ways, including the precision of her bookplate engravings and the demands she placed on her relationships. On June 15, 1913, the Stackpoles' son, Peter, was born in San Francisco.

Stackpole was part of the foursome that founded, early in 1913, the California Society of Etchers (CSE). The other founders were Robert B. Harshe, an etcher and art professor at Stanford University, etcher and educator Pedro Lemos, who taught at the San Francisco Institute of Art, and Gottardo Piazzoni, an Italian-American painter and muralist who was Stackpole's master in France. The CSE exhibited twice in 1913, and grew to 78 artist members and five associate after two years. In 1926, the annual publication listed 46 artist members and 156 associate members: Stackpole was still a member. Decades later, the CSE merged with another group to become the California Society of Printmakers.

Around the same time, Stackpole was commissioned to sculpt architectural features for the 1915 Panama–Pacific International Exposition, a major assignment that was to take two years to complete, even with the aid of assistants. To give a grand entrance portal to the Palace of Varied Industries, he completed a copy of the main entrance to the Hospice of Santa Cruz, built in Toledo, Spain in the 16th century. Stackpole's design replaced the original figures of Catholic saints with figures of industry. His works for the Palace of Varied Industries included "Man with a pick", "Tympanum group of Varied Industries", "New World Receiving Burdens of Old", "Keystone figure", and "Power of Industry". Stackpole also sculpted figures of "Thought" on the columns flanking the half domes of the west facade of the Palace Group. At the Palace of Fine Arts, Stackpole produced a kneeling "Venus" on the Altar of Inspiration. Visitors wishing to view "Venus" were kept some 50 yards (50 m) away by a man-made lagoon.

With Piazzoni, Stackpole went to France again in 1922, taking his family; he enrolled his nine-year-old son in the École alsacienne, a private school in Paris. The two artists wished to investigate the most modern trends in Europe, and they encountered Diego Rivera. While there, Stackpole's marriage unraveled, and he returned to the Bay Area in 1923 with a 24-year-old French still life artist and model named Francine Mazen, nicknamed "Ginette"; his wife and son returned after the school year to take up residence across the bay in Oakland. Stackpole obtained a divorce, and then married Ginette in Mexico.

In late 1923, Stackpole organized a major art exhibit, in partnership with Piazzoni. This was the first large-scale art show in San Francisco since 1915; there had been no expected rush of artists after the Panama-Pacific International Exposition. The exhibit, held in Polk Hall in the Civic Auditorium, was companion to a nearby print exhibit which included Gauguin and Matisse works. Critic and author Laura Bride Powers felt that the event was a disappointment—it displayed "inconspicuous examples" of leading artists, and failed to show any Picasso, avant-garde or Dadaist works.

In 1926, Stackpole delivered the William A. Coleman Fountain to the city of Sacramento, a Moderne work (centrally located in what is now known as Cesar Chavez Park) which celebrated the city's completion of a difficult water filtration project. That same year, Stackpole traveled to Mexico City to see Rivera working on some of his 124 frescoes in the courtyard of the Secretariat of Public Education. Returning with a small Rivera painting, Stackpole gave it to San Francisco Arts Commission president William Gerstle (who was initially unimpressed), and began a several-year effort to bring Rivera to work in California.