He was born and raised in Heidelberg, Grand Duchy of Baden, German Empire (now Baden-Württemberg, Germany). His parents were Louis Carl Moritz Sommerlath (1860–1930), who was born in Chicago, Illinois in the United States, and was from an armigerous family of the German Bourgeoisie, and his wife Erna Sophie Christine Waldau (1864–1944). In the mid-1920s, Walther Sommerlath moved to São Paulo, Brazil where he worked for the steel company Acus Roechling Boulerus do Brasil, a subsidiary in the German steel group Roechling.
On 10 December 1925, Sommerlath married the Brazilian Alice Soares de Toledo (1906–1997), in Santa Cecília, São Paulo. She was the daughter of Arthur Floriano de Toledo and his wife Elisa de Novaes Soares. The couple had four children:Ralf Sommerlath (born 1929)
Walther Ludwig Sommerlath (born 1934)
Hans Jörg Sommerlath (1941–2006)
Silvia Renate Sommerlath (born 23 December 1943), married in 1976 to Carl XVI Gustaf of Sweden
In 1938, Walther Sommerlath left Brazil and returned to Heidelberg. In 1939 he moved to the German capital Berlin. Between 1939 and 1943, Sommerlath ran a company in Berlin that was seized from its Jewish owners by the Nazis. The company manufactured arms to be used in the War. In 1943, Sommerlath’s plant was destroyed by allied bombs. Later that year, the Sommerlath family returned to Heidelberg.
After the war, in 1947 the Sommerlath family returned to Brazil, where Walther Sommerlath worked as the president of the Brazilian subsidiary of the Swedish steel-parts manufacturer Uddeholm. The family finally moved back to Heidelberg in 1957. Walter Sommerlath died in Heidelberg in 1990.
Not very much is publicly known about Sommerlath's Nazi affiliations. Living as a German citizen in São Paulo, Brazil, Sommerlath joined as an expatriate member the German National Socialist Worker's Party, NSDAP/AO, on December 1, 1934, as member no. 3592030. His brother Paul Sommerlath had joined the Party in 1933. Most Germans in Brazil chose not to be members in the party. This is why Brazil's president, Getulio Vargas, found no real opposition when he decided to outlaw it (1938). The Sommerlath brothers remained members of the Nazi party until the party was banned and dissolved by the allies in 1945.
In 1976, when Silvia was to marry King Carl XVI Gustaf of Sweden, the Swedish daily Expressen interviewed Sommerlath about his Nazi background. In the interview, Sommerlath denied that he had any connections with the Nazi Party, saying that his only part of the War was his work at the arms factory in Berlin.
The Swedish Royal Family has declined to give out any information about the Queen's father's role in the war or the name and facts about his company. But on May 16, 2011, Queen Silvia announced that she would probe her father's alleged Nazi ties in reaction to a Swedish TV news magazine.