Irvin McDowell (1818-1885) was a Regular Army officer from Ohio who is best known for commanding the Union army at the First Battle of Bull Run/Manassas. He graduated from the U.S. Military Academy at West Point in 1838, alongside his future opponent in that battle, Pierre Gustave Toutant-Beauregard. He fought in the Mexican-American War, and served on the staff of General Winfield Scott just prior to the outbreak of the Civil War.
When that war came, he was promoted to brigadier general and given command of the Army of Northeastern Virginia, assigned with invading Virginia from Washington, DC. He was a reluctant commander in charge of raw recruits, and this combined with other factors led to his ignominious defeat at Bull Run. McDowell was relegated to lesser commands for the remainder of the war and spent his twilight years in California.