Sonja Härdin, born 1945, is a Swedish illustrator. She illustrated all Bert books in the old series However, the first Bert book was illustrated by Sören Olsson. She also illustrated the reversion edition of the first Bert book. She gave Bert and the other figures in the Bert Diaries their cahracteristic looks. From "Berts bekännelser" the style was changed. Darker images were added. She has also illustrated articles in Kamratposten. Also, she illustrated school coursebooks like "Nya Min matematik". Nya Min matematik is a series of mathematics books for Swedish elementary schools. She has also illustrated Trafik-Trolle.