Eugen Langen (1833-1895) was a German entrepreneur, engineer and inventor, involved in the development of the petrol engine and the Wuppertal monorail.
In 1857 he worked in his father's sugar factory, JJ Langen & Söhne, after an extensive technical training at the Polytechnic institute in Karlsruhe.
1864 Langen met Nikolaus August Otto. Otto was working on improvements to the gas engine invented by Etienne Lenoir. The technically trained Langen recognized the potential of Otto's development, and one month after the meeting, founded the first engine factory in the world, NA Otto & Cie.
At the 1867 Paris World Exhibition their improved engine was awarded the Grand Prize.
After this first factory went bankrupt, Langen founded a new company for the construction of gas engines, the Deutz gas engine factory, which later became the group Kloeckner-Humboldt-Deutz (KHD). This became today's Deutz AG. Langen invented and applied new methods of production in the KHD factory.
In the field of rail transport equipment, Langen was co-owner and engineer of the Cologne Waggonfabrik van der Zypen & Charlier.
He started the Wuppertal monorail, a suspension railway system, in 1894.