An illustrator draws or paints the pictures that live with a text: a children’s story, a school book, a magazine article, a package. The pictures are there to help you see the words. It is a job word. It is not the same as a painter who shows work in a gallery, though the same person may do both. Though actually illustrate can also mean “explain with an example,” an illustrator is almost always the picture-maker, not the explainer.