I think the earliest I came to contact with an artist was Victor Vasarely, 'father' of op-art. http://www.op-art.co.uk/victor-vasarely/ This was the museum we lived the closest and I used to go there as a kid, later I kept doing 3D looking 'drawings' with a ruler and pencils, coloring every second piece, so it looked even more cool. It was easy to do, but the result was fascinating and I could get totally lost concentrating putting the lines in the correct order. (I know I linked to a whole site, but it's hard to pick just 1 work and I was also suprised there's a whole site for op-art, so I thought I share it.)