Leo Leonhard was born in Leipzig in 1939. After his German studies in Marburg, he studied painting and drawing at the Düsseldorf Art School. He was an art teacher and trainer in Darmstadt and Bensheim and been a professor in drawing and illustration with the University of Applied Sciences in Mainz.
He is known for his illustrations for the 1972 picture book 'Rüssel in Komikland', that was written by Otto Jägersberg and combined comic elements and references to art history. Leonhard and Jägersberg revived the book's character 'Flabby Jack' for the follow-ups 'Glücksucher in Venedig' (Melzer Verlag, 1974) and 'Leben & Traum mit Schellenfusz' (Melzer, 1975).
