Didier Kassaï was born in Sibut. His career in cartoons began in 1997 when he got a job at the daily newspaper Le Perroquet. He studied to become a comic artist, first in Africa (Bangui, Libreville, Yaoundé and Kinshasa), and later in Brussels. In 1999, the work of Kassaï appeared at the Gabonese festival Journées Africaines de la Bande Dessinée. One year after that, he contributed to the collection album 'A l'Ombre du Baobab', which was published on the occasion of a group exhibition at the festival of Angoulême (France). He also participated in Africa Comics 2003 in Italy and in Shege in Cameroon.
In 2005, he made educational comics for the Educa 2000 project in Bangui, for which he and Olivier Bombasaro created the character of 'Gipépé le Pygmée'. The other published episodes in this series are 'Gipépé et le bébé', 'Gipépé et la fièvre remonla', 'Gipépé et les exploiteurs de bois' and 'Aventures en Centrafrique'. These publications were succeeded by the album 'Les Exclus', published by the Canadian publishing company TNT, and a scenario by Clotaire Ben Seba.