Mary Oosterdijk was a female artist working for the Toonder Studios in the mid 1940s. She participated in the animation of the film production 'Tom Puss, Das Geheimnis der Grotte' (1944). Prior to this, she was one of Marten Toonder's colleagues at the Nederlandse Rotogravure Maatschappij in Leiden, where she made illustrations for magazines like Cinema en Theater under the pen name May.
Shortly after World War II, she possibly illustrated the second, third and fourth 'Kappie' story. The texts of 'Kappie en het neveleiland', 'Kappie in China' and 'Kappie en de God van duizend vrezen' were written by Phiny Dick and published in Dutch newspapers from 1946. Oosterdijk was later active as an illustrator of fairytales, and she has participated in productions by Joop Geesink's Dollywood studios.