He became famous as the protagonist of a German TV mini series based on Jack London's the Sea-Wolf (which was sold into many countries) and starred later on successfully in another German TV series based on Jules Verne's Michael Strogoff.

His breakthrough was in 1971 with the TV series Der Seewolf, based on Jack London's novel The Sea-Wolf, where he played the evil-minded Captain Larsen.

Later he played in several spaghetti westerns along with Bud Spencer, Franco Nero and Charlton Heston.

Toward the end of his career he was affected by Parkinson's disease and weakened by a regimen of heavy medication.

[7] Harmstorf's girlfriend confirmed that the actor had obviously already been dismayed after he had read this article, even before the news had been partly quoted on Germany's popular TV channel RTL Television.