His international breakthrough was his portrayal of the good-hearted and sympathetic U-boat Commander "Der Alte" ("Old Man") in the 1981 war film Das Boot.

[1] He is also known for his roles in The Lost Honour of Katharina Blum (1975), Dune (1984), Beverly Hills Cop II (1987), Twin Peaks: Fire Walk with Me (1992), In the Mouth of Madness (1994), The English Patient (1996), Air Force One (1997), The Da Vinci Code (2006), and for playing Sergei Bazhaev on the eighth season of 24 (2010).

[2][better source needed] Prochnow portrayed the good-hearted and sympathetic U-boat Commander "Der Alte" ("Old Man") in the 1981 war film Das Boot.

After the retirement of Stallone's long-time voice actor Thomas Danneberg, Prochnow assumed this job in 2018 with Creed II.

[4] In the early 1980s, Prochnow was in a relationship with Austrian actress Antonia Reininghaus [de], who fatally poisoned their 7-year-old daughter, Johanna, in 1987.