François (Frank) Sels studied art in Antwerp, and then he worked in a printing firm for a short while. He joined Studio Vandersteen in 1963, and succeeded Karel Verschuere on 'Karl May' and on 'De Rode Ridder', introducing the King Arthur-cycle in the series.
Starting in 1964, he illustrated several comics in the magazines Ons Land and Ohee, working with scripts by Lorenzo Wadlin and his childhood friend Hugo Renaerts. He specialized in historical, viking and western stories, such as 'Mister Grizzly', 'Abraham Lincoln', 'De Ilias','Tall Bull' and 'Kleine Antilope. For magazine 't Kapoentje he worked on 'Arkulleke', 'Bongo Tegen de Kux Klan', 'Kleine Antilope' and 'De Avonturen van de Zeearend'.
In 1966, Sels resigned from Vandersteen, only to return when he didn't find work with publisher Het Volk. He got a job at the 'Bessy' studio, where he and Edgard Gastmans were responsible for the production of stories for Bastei Verlag in Germany. For a period of two years, Sels and Gastmans produced a complete 'Bessy' story almost every week.