Hilke Mayer is the pseudonym of Silke and Heike Mayer, two sisters from Munich. They’re not just friends with Olga, but also with Kai Pannen, a Hamburg-based illustrator and animator. Silke Mayer, born in 1973, works as an editor and holds a diploma in psychology – she has practised as a gestalt- and client-centred therapist. Heike Mayer, born in 1969, also works as an editor and has practised Zen meditation for many years.