Hugo Schmeisser began his career with his firearms engineer father Louis Schmeisser (1848-1917) at Theodor Bergmann's munitions factory in Suhl, Germany. Hugo worked at Bergmann's until about 1921 when Lignose took over, had a close association with his brother Hans at the Haenel weapons factory where they seem to have been contractors. Improved the MP-40 at Haenel (redesigned as the selective fire MP-41) and headed the MKb 42 (early MP-44) development. Captured in 1945, traded to the Russians who he claimed made him participate in the development of their AK-47. Mikhail Kalashnikov denied any foreign influence on his designs, Schmeisser said he gave them "ideas." Soviet prisoner 1945-1952, the East Germans claimed Hugo died of pneumonia in 1953.
The MP-18 was designed by Louis and Hugo Schmeisser, 10,000 were issued from 1916 to the end of WWI.
More than 1,000,000 MP-40 were issued during WWII, developed at Erma by Heinrich Vollmer (from earlier designs Schmeisser was involved in). The Schmeisser family and Haenel held manufacturing patents involving part of the stamped metal fabrication process and detachable ribbed magazines.
500,000 MP-44 were issued during WWII.
100,000,000 AK-47 have been built since WWII.
Some view the Kalashnikov as a redesigned (upside down) M1 Garand put together like an MP-44, though that's probably an oversimplification of the facts.
Some pictures I copied from the modern day Schmeisser factory history page: Schmeisser GMBH Suhl (defunct as of 2003).
Hugo posing with what looks like a Maxim Model 08/15 water cooled light machine gun.
Hugo and Hans? These weren't captioned.
Hugo (zoomed in from a group shot).
Hugo with an MP-18, there's a couple more pictures but they're of his country home.