Lysander Cutler (February 16, 1807 – July 30, 1866) was an American businessman, educator, politician, and Wisconsin pioneer. He served as a Union Army officer through almost the entire American Civil War, notably commanding the famed Iron Brigade of the Army of the Potomac. He rose to the rank of brigadier ganeral and received an honorary brevet to major general. Earlier in his career, he was a member of the Maine Senate.

Cutler was born in Royalston, Massachusetts, the son of a farmer. Despite objections from his father, he desired a better education than the rudimentary courses he received in the local school, so he studied surveying and then began a career as a schoolmaster. Moving to Dexter, Maine, at the age of 21, he was forced to confront unruly pupils who had "flogged and ejected" the last several teachers who had attempted to discipline them. Cutler established his reputation by spending his first day in the "thorough flogging of every bully in the school."

Although he received some military experience fighting Indians as a colonel in the Maine militia in the 1830s, the majority of his time before the Civil War was engaged in a variety of business pursuits. He started a woolen mill, a foundry, a flour mill, and a sawmill, becoming very wealthy in the process. Cutler invested in various factories and in tenement housing.

He was prominent in civic affairs as a selectman, director of a railroad, trustee of Tufts College, and a member of the Maine State Senate in 1841. Cutler's woolen mill, built in 1843, burned to the ground in 1853, causing him to lose his entire investment. The financial panic of 1856 and depression of 1857 ruined him financially, and he decided to leave Maine and move to Milwaukee, Wisconsin, to restart his career.

In Wisconsin, Cutler worked as a claims investigator for a mining company. He was required to make frequent trips into Indian territory, where he was often threatened with ambush and death. The mining company eventually failed, but a grain business that he founded in Milwaukee provided him with a living.

In the first summer of the Civil War, Cutler, a respected 54-year-old businessman and Indian-fighter, was commissioned colonel of the 6th Wisconsin Infantry on July 16, 1861. This regiment would eventually become one of the units to comprise the famous Iron Brigade of the Army of the Potomac.

During the fall and winter, he got off to a bad start as a commander, alienating his junior officers by insisting that they pass examinations on military topics, and removing them from command if he was displeased with the results. Many men of the regiment were of recent immigrant status and he sometimes enraged the enlisted men of the company by replacing their officers with men of different national backgrounds, and sometimes speaking different languages. Despite these problems, Cutler was elevated to temporary brigade command in the I Corps of the Army of the Potomac on March 13, 1862.

Cutler's men rejoiced when this temporary position was filled by Brig. Gen. John Gibbon that summer. The regiment's first significant action was the Second Battle of Bull Run, where he demonstrated that he was a tenacious fighter. One soldier in his regiment said that he was "rugged as a wolf." During the fighting against Stonewall Jackson at Brawner's Farm, Cutler was severely wounded in the right thigh, causing him to miss the Maryland Campaign and the Battle of Antietam of September 1862.