Hillen was born in Brussels, Belgium in 1819 and immigrated to the United States. He lived in Philadelphia in the early 1850s and joined the Union Army in 1861. He was wounded in 1862 and discharged as disabled. In the same year, his scenes of war in West Virginia were published in Harper’s Weekly. He worked as a “special artist” for Frank Leslie’s Illustrated Newspaper from 1862 to 1865, which published his drawings of battles and camp life in Virginia, Georgia, and Tennessee. The Becker Collection contains drawings done by Hillen in Alabama and Georgia between 1863 and 1864.