Felix Agnus was born on May 5, 1839, in Lyons, France, the child of Etienne and Anne (Bernerra) Agnus. Before 1861, Agnus led a remarkable life, working as an artist, merchant sailor, and soldier. He attended the College of Jolie Clair, near Montrouge, but left college for the sea. During of four years of service, Agnus sailed around the world, visiting St. Helena, West Africa, the Cape of Good Hope, Madagascar, Chile, and Peru before returning to France via Cape Horn. Upon his return to France, Agnus spent three years studying sculpture but he abandoned his studies for the Austrian War, during which he served in the 3rd Regiment of Zouaves. On May 20, 1859, he participated in the Battle of Montebello and was later detailed to Garibaldi's Corps in the Italian Lakes region. After the war, Agnus emigrated to the United States, where he temporarily settled in Newport, Rhode Island. Agnus subsequently moved to New York City, where he worked as a sculptor and chaser with Tiffany and Company.
In the aftermath of the Confederate attack on Fort Sumter, President Abraham Lincoln issued a call for 75,000 volunteers, and Agnus, already an experienced soldier, enlisted in the federal army. On April 15, 1861, he volunteered as a private in the 5th New York Infantry, Duryee's Zouves. The 5th New York wore the colorful uniforms of the French colonial forces, or "zouaves," with bright red baggy pants, white turbans, and short jackets. The regiment's uniforms, precise maneuvers, and incredible courage made Duryee's Zouaves one of the most celebrated units in the Union Army. Speaking of the 5th New York, General George Sykes said "I doubt whether it had an equal and certainly no superior among all the regiments of the Army of the Potomac."
Agnus built an impressive military career, as evidenced by his meteoric rise through the ranks. He was mustered into service as a sergeant of Company "H" on May 9, 1861. On June 10, 1861, Agnus fought in the Battle of Big Bethel, which was the first land battle of the war. During the engagement, Agnus distinguished himself by saving Captain Judson Kilpatrick, who later became a prominent cavalry officer. In recognition of his courage, Agnus received a series of promotions. He was promoted to first sergeant of Company "H" on July 20, 1861; to second lieutenant on September 6, 1861; and to first lieutenant of Company "D" on July 8, 1862. On June 27, 1862, Agnus participated in the Battle of Gaines's Mill, where he received a severe wound to the shoulder. After the Peninsula Campaign, the 5th New York was transferred to Baltimore, Maryland, and stationed on Federal Hill. While the regiment maintained order in the city, Agnus convalesced at the home of Charles C. Fulton, publisher of the Baltimore American. It was here, presumably, that Agnus courted Fulton's daughter, Annie, whom he married on December 13, 1864.
After recovering from his wounds, Agnus, along with several convalescing officers, recruited for the 165th New York Regiment of Volunteers, the 2nd Duryee Zouaves. Agnus, who commanded the regiment's color company, served with the regiment for the remainder of the conflict. During 1862 and 1863, the 165th New York was garrisoned at New Orleans and Baton Rouge, Louisiana. On May 27, 1863, Agnus was wounded during an assault on Port Hudson. He remained with his regiment after the injury and was among the Federal officers who volunteered for the proposed effort to capture Port Hudson by storm. Agnus's gallantry during the campaign earned him a promotion to major on September 2, 1863. The following year, Agnus, now a lieutenant-colonel, commanded the 165th New York during General Philip Sheridan's Shenandoah Valley Campaign. More promotions followed the Valley Campaign. Agnus was promoted Brevet Colonel, and, on March 13, 1865, he was promoted to Brevet Brigadier General. During the spring and summer of 1865, the 165th New York was stationed in the Deep South, where it participated in the occupation of Savannah and dismantled Confederate batteries and fortifications in South Carolina, Georgia, and Florida. Agnus resigned his commission on July 26, 1865.
Following the Confederate surrender, Agnus pursued careers in newspaper publishing and politics. On July 4, 1869, he was promoted to business manager of the Baltimore American. When Charles Fulton died in 1883, Agnus was promoted to publisher and sole manager of the newspaper. Agnus expanded the business on August 17, 1908, when he founded the Baltimore Star. Agnus operated these businesses until November 1920, when he sold both newspapers to Frank A. Munsey. In addition to managing the Baltimore American and Baltimore Star, Agnus was active in Republican politics. Although never a candidate for public office, he held numerous civic posts. He served twice as a member of the Board of Visitors of West Point; he was chairman of the Chesapeake and Delaware Canal Commission and was a member of the commission that built the Baltimore Courthouse. Agnus also participated in the Grand Army of the Republic, a veterans' organization for Union soldiers. Agnus recounted his military career in a collection of short stories published in 1894 entitled A Woman of War. He also published a reference book entitled Book of Maryland: Men and Institutions in 1920. He died on October 31, 1925, at the age of eighty-six.
Felix Agnus continued to make news after his death. He was buried in Druid Ridge Cemetery in Pikesville, Maryland, underneath a bronze statue of an angel, which he had purchased a few years earlier. This statue turned out to be a copy of an earlier work by Augustus St. Gaudens that was commissioned by Henry Adams for a memorial for his wife. Over the years, an interesting folklore developed surrounding the Agnus statue, which was nicknamed "Black Aggie." People claimed that it had supernatural powers and it was frequently vandalized. In 1967, Agnus's descendents removed the statue from the gravesite and donated it to the Smithsonian. After many years in storage, the statue may now be seen at the Federal Courts building in Washington, in the rear courtyard of the Dolly Madison house.