Nathaniel Lyon (July 14, 1818 – August 10, 1861) was a United States Army officer who was the first Union general to be killed in the American Civil War. He is noted for his actions in Missouri in 1861, at the beginning of the conflict, to forestall secret secessionist plans of the governor Claiborne Jackson.
He had fought in the Second Seminole War in Florida and the Mexican–American War.
In 1850 he co-led the Bloody Island Massacre of 60–200 Pomo Native American old men, women, and children as part of the wider California genocide. Several days later, Lyon was responsible for another massacre in Cokadjal, killing 75 to 100 Native Americans, albeit the number was likely double.
After being assigned to Kansas, where many residents were divided about slavery and the Union, he developed strong pro-Union views. In February 1861, Lyon was made commander of the Union arsenal in St. Louis in Missouri, another divided state. Suspicious of governor Jackson, who was working with Jefferson Davis on a secret plan for secession, Lyon forced the surrender of the pro-Confederate militia.
Some civilians rioted and Lyon’s troops fired into the crowd, which came to be known as the Camp Jackson Affair. Lyon was promoted brigadier-general and given command of Union troops in Missouri. He was killed at the Battle of Wilson’s Creek, while trying to rally his outnumbered soldiers. Despite his death during the first year of the war, Lyon’s efforts prevented the State of Missouri from joining the Confederacy.
Source: Wikipedia