Born in Duisburg, Krug moved to East Germany at the age of 13, and worked at a steel plant before beginning his acting career on the stage and, ultimately, in film.
By the end of the 1950s he had several film roles, and in 1960 he appeared in Frank Beyer's successful war movie Fünf Patronenhülsen (Five Cartridges).
Krug also achieved notability as a popular jazz singer, often in collaboration with composer Günther Fischer.
[citation needed] After moving back to West Germany he very soon got new roles as an actor but very rarely sang in public for a long time.
In the 1980s and 1990s, he also starred as Hauptkommissar Paul Stoever in the Tatort series of TV crime movies, which would eventually run for forty installments in total.