Kruis started his own comics career drawing Prins Freddie for the magazine De Havenloods,[2] but became famous thanks to his series of one-pagers called Jan, Jans en de Kinderen (Jack, Jacky and the Juniors).

In German-speaking Switzerland it appeared in the magazine Spick which targeted children and teenagers; and in Germany Favorit published it for some time under the name "Ulli, Ulla und die Kinder".

He also had a gag comic named Gregor running in Tintin, between 1965 and 1966, which was later reprinted in Pep.

In 2013 his career was celebrated in a one-off glossy-zine; this includes previously unpublished gags of a comic about an infant punk raised by a gay couple; hence the nickname "Jan, Jan en de Kinderen" ("Jack, Jack and the Juniors").

[8] On 20 January 2017, a good friend of the family informed the press about his death on the previous day.