Harry Jackson, a Marine combat artist who turned his back on a promising career as an Abstract Expressionist painter to become a prominent realist artist known for his paintings and bronze sculptures of cowboys and Indians, died on Monday in Sheridan, Wyo. He was 87 and lived in Cody, Wyo., and Camaiore, Italy.

His death was confirmed by his son Matthew.

Mr. Jackson, infatuated by the West from early childhood, headed to Wyoming from his hometown, Chicago, at 14 and found work as a ranch hand, working his way up to cowboy. There, when not tending cattle, he turned out shoot-’em-up sketches in the manner of Frederic Remington.

After enlisting in the Marine Corps at 18, he was assigned as a sketch artist to the Fifth Amphibious Corps. He was seriously wounded in the battle for Betio Island in the Tarawa atoll in November 1943 and again at Saipan, for which he was awarded the Purple Heart. Because of his war injuries, he struggled throughout his life with life-threatening epileptic seizures and severe mood disorders.

After being shipped to Los Angeles, he was made an official Marine Corps combat artist, with the assignment to execute drawings and paintings depicting, as he put it, “my bloodiest close-combat experiences.” This he did in paintings like “Tarawa-Betio” (1944), now in the collection of the National Museum of the Marine Corps in Triangle, Va.

After seeing the Jackson Pollock painting “The Moon-Woman Cuts the Circle,” Mr. Jackson underwent an artistic conversion. The painting, he said, “shot the first crack of daylight into my blocked-off brain.” He moved to New York, where he became a close friend of Pollock’s and began painting in the Abstract Expressionist style.

He quickly gained notice as an artist to watch when Meyer Schapiro and Clement Greenberg included him in their “Talent 1950” exhibition at the Kootz Gallery, and over the next several years he exhibited at Tibor de Nagy, a nerve center of second-generation Abstract Expressionism.