Léon Henri Nagant de Deuxchaisnes was a Belgian automobile and arms designer.
Born in Liège in 1833, he and his brother Émile began working in the fabrication and repair business in 1859, and often found themselves repairing broken firearms. They met Samuel and Eliphalet Remington in 1867 as they were moving around Europe in an attempt to market their Rolling Block rifles around said continent, along with attempting to find subcontractors who would produce the weapons in the area.
On their meeting, the Remingtons were highly impressed by the craftsmanship of the brothers that he decided to hire them as one of his subcontractors for his new Rolling Block rifle; the brothers would found their firm, E. & L. Nagant Frères, in 1859, and would end up producing 5,000 for the Papal Zouaves. The brothers would then design a number of other different firearms using the same basic rolling block action, along with various revolvers and shotguns.
In 1888, Nagant were contacted by the Russians to have them develop a new rifle with Major General Sergei Mosin; this would become the Mosin-Nagant. After designing the weapon, he returned to Liège. Both brothers were called upon to design a new revolver for the Russians when it came time for them to replace the old Smith & Wesson revolvers that were in use at the time; they came up with the Nagant M1895, which was swiftly adopted.
By 1896, Émile had fallen ill and the Nagant business was quickly dissolved; after which, Nagant switched his focus to the production of automobiles. He died in Liège in 1900, aged 66.