Born in The Hague, Gerard van Straaten was the brother of famous Dutch cartoonist Peter van Straaten. Although mainly an illustrator, he was active in the comics field between 1948 and 1967. Van Straaten studied art in Arnhem and worked for an advertising firm, before joining the Toonder Studios. There, he drew backgrounds at the animation department, but also comics for Tom Poes Weekblad. His first comics work was 'Rex Rijvers', that appeared in Het Vrije Volk in 1948. This was followed by 'Pedro de Cania' and 'Marco Polo' (which he took over from Cees van de Weert) in Tom Poes Weekblad in the following year.
Using the pseudonym Sidoan, Van Straaten made advertising strips such as 'Stuurman Steven' for Niemeyer Shag (1951) and 'De Avonturen van Bert en Bettie Brinta' for Brinta porridge (1956, with text by A.D. Hildebrand). For the magazine Ping, a publication of the Rabobank, he drew comics like 'Ping Li-Ping, de Keizerlijke Schatbewaarder', 'Ruimtepatrouille SP-3' and 'Buffalo Kid' with scripts by Harry Baljet during the 1960s.
Van Straaten started working for publisher Kluitman in 1953. He is best known as the illustrator of the famous children's book series 'De Kameleon' by Hotze de Roos, but he has also illustrated 'Swiebertje' and 'Bakkertje Deeg' books. In addition, he made illustrations for magazines like Tom Poes Weekblad, Pep and Donald Duck. Gerard van Straaten continued to make illustrations for Kluitman until the late 1990s.