Renaat Demoen started his career working in a shoe-factory and later at a printer in Izegem. After this, he started illustrating, and in 1942 he met Nonkel Fons, who asked him to draw for De Goede Pers, the publishing branch of the abbey of Averbode. Together, they made several comics, including the colorful 'Auto-stop'. After the death of Demoen's father, he came to live in the abbey itself. After he got married, he moved to the village of Averbode.
In 1945, Demoen drew his first comic for Zonneland, 'Jack Persson', followed by 'Spits' and eventually the popular 'Johnny' in 1947 (which he took over from Jan Waterschoot). With writer John Flanders, he made 'De Zwarte Veroveraar'. Between 1945 and 1959, Demoen drew fifteen comic series for Zonneland and its French language counterpart Petits Belges, which stand out for their experimental style and a distinct influence of Hergé. After 1959, Demoen devoted himself to illustrations only, which he did until 1969.
Muss Detective (Petits Belges, 23-6-1946)