Henry Halleck
The regiment is unusual in that it has two official designation. It was officially raised as "Merrill's Horse", and is usually referred to by that designation in period U.S. Army Records. However, after General Fremont was replaced as commander of the Western Department by Major General Henry Halleck received a second official designation at the 2nd Missouri Volunteer Cavalry. However, in almost all contemporary reports and records the regiment continued to be referred to as Merrill's Horse.