Walter was born to Eduard and Elisabeth Höpken on March 3, 1924 and raised in Germany alongside his five siblings; Gisela, Johann, Karl, Wilhelm and Peter.

Walter served in the Reich Labour Service during World War II until he contracted tuberculosis. Although he fully recovered from this illness, he was deemed unfit for military service. In 1942, he began studying medicine in Graz, Austria and continued his studies in Düsseldorf, Germany after the war. He wrote his state exams in 1947.

Afterwards, he accepted a position as an intern at a hospital in Lüneburg, Germany and wrote his medical exams. In 1949, Walter worked as a practical hygienist and as a scientific researcher in the area of bacteriology and virology. Later he worked as an assistant at the Medizinaluntersuchungsamt in Lüneburg and Osnabrück, Germany and then successively accepted positions at the Institute for Cellular Research and Tissue Cultivation, the Robert Koch Institute and at the Lower Saxon Medizinaluntersuchungsamt as the Chief Medical Officer after 1954. At some point, Walter also spent half a year working at John Hopkins University in Baltimore, Maryland after receiving a scholarship. Walter travelled frequently for his work and specialized in researching influenza viruses.

Sometime before 1960, Walter married a woman in Gratz, Austria and had two children; Fritz and Anne. Fritz was considered a good student and enjoyed studying German and English. He hoped to become a lecturer. Anne became a nurse and moved from Gratz, Austria to Hanover, Germany to care for her stepmother. Afterwards, Anne moved to Toronto and travelled to Canada by ship. She met a young Swiss man on the ship and they married a year later. Anne and her husband eventually moved to Switzerland. Walter's first wife's name is unknown.

In 1960, Walter married for the second time and had a son named Jens (b. 1962). His second wife's name is unknown.

It appears that Walter also had another son named Thomas (b. April 13, 1953).