Nathaniel Lyon (July 14, 1818 – August 10, 1861) is the first Union general to be killed in the American Civil War and is noted for his actions in the state of Missouri at the beginning of the conflict.

Lyon is a controversial figure in American history.

Some credit his quick action and hard line Unionism for stopping the Missouri secession movement.

Others question his influence peddling and his role in events such as the Camp Jackson Affair, which inflames many Missourians on the secession issue.

He graduated from the Military Academy 11th out of a class of 52 in 1841.

He fights in the Second Seminole War and in the Mexican–American War.

During the War with Mexico, he receives several brevet promotions for gallantry under fire at the battles of Mexico City, Contreras, and Churubusco.

He is then sent to posts in California where he participates in the 1850 Bloody Island Massacre against the Pomo Native Americans.

He is reassigned to Fort Riley in Kansas, where he begins to develop strong support for the Union as a result of the political climate developing in the state.

In February 1861, Lyon is made commander of the Union arsenal in St. Louis, Missouri, where tensions grow between the Union soldiers stationed there and the secessionist governor of the state, Claiborne Jackson.

When the Civil War breaks out, Jackson refuses to send volunteers from the state to fight for Abraham Lincoln.

Instead, Jackson has the militia muster outside the city to begin training in preparation to join Confederate forces.

On May 10, 1861, Lyon and his troops surround  the pro-Confederate Missouri militia under General D. M. Frost, and force its surrender.

While marching his captured prisoners through St. Louis, citizens begin to riot, leading to the Camp Jackson Affair.

Lyon orders his troops to fire into the rioters.

On May 17, Lyon is promoted to brigadier general and is given command of Union troops in Missouri.

He now leads his troops into a series of skirmishes with the Missouri State Guard and Confederate Army.

On August 10, 1861 the Union forces are defeated by a combined force of the Missouri Militia and Confederate troops under the command of Benjamin McCulloch and Sterling Price near Springfield, Missouri, at the Battle of Wilson’s Creek.

Lyon is killed while trying to rally his outnumbered soldiers.

However, Lyon’s efforts prevent the State of Missouri from joining the Confederacy.