Born in Sweden on April 20, 1893. In 1912 Gren (né Ahgren) sailed for Australia and intended to stay for only a short while. Due to the upheaval of WWI, it became necessary for him to remain in Sydney.
In 1919 he immigrated to the U.S. and spent his first few years in NYC where he worked as a designer for a pattern manufacturer. By 1925 he had moved to southern California where he studied art with Stanton MacDonald-Wright. He lived in Los Angeles for only a few years before making his final move to San Francisco in the late 1920s.
Around 1930 he destroyed all of his earlier paintings; any works now extant are those done during the 1930s. During that period he produced lithographs for the WPA project. His oils are mostly still lifes, landscapes, and scenes from San Francisco.