Hugo Schmeisser began his career working with his firearms engineer father Louis Schmeisser (1848-1917) at Theodor Bergmann's factory in Suhl, Germany. After the war he continued designing and later had a close association with his brother Hans at the Haenel factory, where he improved the MP40 (redesigned as the selective fire MP41) and headed the MKb 42 (early MP44) 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 told Western spies that he gave them ideas. Soviet prisoner from 1945 to 1952, the East Germans said Schmeisser died of pneumonia in 1953. In 2009, Kalashnikov allegedly admitted that Schmeisser helped.
The MP18 was designed by Louis and Hugo Schmeisser, 10,000 were issued to the end of WWI, more after that.
More than 1,000,000 MP40 were issued during WWII, developed at Erma by Heinrich Vollmer (from earlier designs that 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 MP44 were issued during WWII.
100,000,000 AK-47 have been built since WWII. Schmeisser might have contributed in some way.Some view the Kalashnikov as a redesigned (upside down) M1 Garand put together like an MP44, though that's probably an oversimplification of the facts.
Some pictures copied from the modern day Schmeisser GMBH Suhl history page (defunct as of 2003).
Hugo posing with what looks like a Maxim Model 08/15 water cooled light machine gun.
Hugo and family? These weren't captioned.
Hugo (zoomed in from a group shot).
Hugo with an MP18. There's a couple more pictures of his country home.