Olivier Grojnowski studied at the comics school in Angoulême together with Baron Brumaire and Hubert Chevillard. He began his career as an illustrator at the Version Originale agency. He also worked in animation, notably on Margerin's 'Manu' series. He started working for Spirou in 1995, making several cartoons and illustrations. A year later, O'Groj started his series 'Les Dragz' with Corcal. This series, about a dragon-like father and son, is full of absurd situations and crazy creatures.
In 1999, Casterman published his solo album 'La Semaine des 7 Noël', a futuristic book about France in a dictatorship under Santa Claus in the year 2041. In 2004, he began 'Nestor et Polux' in cooperation with Fabrice Tarrin and Fred Neidhardt in the relaunched Pif Gadget. A first album appeared in November 2005. For L'Echo des Savanes, he makes the gag strip 'Les Krazbek's'.