When I was little, I was afraid of the illustrations by Dutch illustrator Carl Hollander (1934-1995)
Even the most friendly scenes had a dark undertone, as if madness could break out at any moment.
Maybe it was just that the illustrations seem to be black and white drawings, with colour added as an afterthought, making them a bit gloomy.
Anyway, I appreciate his work now immensely.
(And I was easily scared: Fiep Westendorp's Jip and Janneke freaked me out as they had big black heads with little holes instead of eyes)