Klaus Janson was born in Coburg, Germany. He emigrated to the US in 1957 and settled in Connecticut, discovering comics very shortly thereafter. Janson made a professional debut for Marvel in 1973, inking the artwork of Rich Buckler for the series called 'The Black Panther', that were published in Jungle Action. During years he continued inking the diverse Marvel titles, like 'the Defenders', 'Deathlock', 'Battlestar Galactita' and 'Howard Duck'. But Janson main series was 'Daredevil'. In this period he inkted to Gene Colan, Gil Kane, Carmine Infantino and Frank Miller. Working with Miller, Janson changed his ink style.
Later on Janson decided also to take care of the pencils. With Miller, Janson worked on the influential mini-series 'The Dark Knight Returns'. After Janson ended his work on 'Daredevil', he had developed a constant work as a sketcher, were he devolped a Gothic like style. He also did a lot of work on 'The Punisher', 'Spawn' and an adventure of Batman in five episodes which was scripted by Grant Morrison.