Gustav Lorentzen
- Birthday: 1947-09-28
- Deathday: 2010-04-21
- Place of birth: Bergen, Norway
- Also know as: Gustav Fredrik Lorentzen
Gustav Fredrik Lorentzen was a Norwegian musician, comedian and writer. He is best known to most as his alter ego "Ludvigsen" in the duo Knutsen & Ludvigsen (1970–1986).
