Throughout the 1930s and 1940s, Waltari worked as a journalist and critic, writing for a number of newspapers and magazines and travelling widely in Europe. He directed the magazine "Suomen Kuvalehti". At the same time, he kept writing books in many genres, moving easily from one literary field to another. He had a very busy schedule and strict work ethic. He also suffered from manic-depressive psychosis and became depressed after completion of a book, sometimes to the extent of needing hospital treatment; in his manic phases he did his writing. He participated, and often succeeded, in literary competitions to prove the quality of his work to critics. One of these competitions gave rise to one of his most popular characters, Inspector Palmu, a gruff detective of the Helsinki police department, who starred in three mystery novels, all of which were filmed (a fourth film was made without Waltari involved). Waltari also scripted the popular cartoon "Kieku ja Kaiku" and wrote "Aiotko kirjailijaksi", a guidebook for aspiring writers that influenced many younger writers such as Kalle Päätalo.