Gustav was born in 1843, a son of Carl Heinrich Sanftleben and his wife, Catharina Maria Koester.  Gustav, his wife Maria "Mary" Dorthea Doescher, and their first three children lived in the village of Ritzbuettel, adjacent to the town of Cuxhaven on the coast of the North Sea until 1880.

U.S. Census records indicate that Gustav and his family arrived in the United States in 1880, however family tradition has always suggested Gustav first came to America in the late 1870s and that once he was settled in St. Louis, Missouri, he returned to Ritzbuettel to bring back Mary and the children in 1880.  Gustav and Mary had four more children born in the United States.

Gustav, a locksmith and sheetmetal pattern maker, died in 1911.  Mary was ninety years old when she died in 1943.