At the age of 16, he was sent to a premilitary training camp of the Hitler Youth and then drafted to the Reich Labour Service.

[1][2] After returning home in 1947, Simon took private acting lessons with Karl Meixner in the Hebbel Theater in Berlin.

At the same year, in spite of his inexperience, he was chosen to portray Ernst Thälmann in Kurt Maetzig's two-part propaganda epic about the communist leader's life.

[4] Simon received the National Prize first class for his work on the first part,[5] and the Best Actor Award in the 1956 Karlovy Vary International Film Festival for his appearance in the second.

[6] He joined the country's Socialist Unity Party of Germany (SED / Sozialistische Einheitspartei Deutschlands) in 1954[7] and became a member of the DEFA Studio's management.