[1] He apprenticed to Hans Martens in Freiburg, Germany and worked in Karlsruhe, Wiesbaden and Lode.
On his trip to America he met Pauline Wittlinger, the daughter of a watchmaker who lived in Delaware, Ohio.
In 1874 Gruen filed U.S. patent 157,913 for a 'safety' pinion that prevented damage to a pocket-watch movement if the mainspring broke.
In 1894 Gruen left the Columbus Watch Company, which later bankrupted following the Panic of 1893.
In 1911 Gruen died suddenly on the steamship SS Berlin on a business trip to Italy with his son Fred, near Algiers.