Jon Gnagy was of a certain time. He was a fad for a while. He made a lot of average middle class kids out in America try drawing, when they would never have done so otherwise.
I remember his charts and explanations of perspective, how to draw something so it would look realistic off in the distance in the drawing. I couldn't do it, but it was interesting to read and think about.
His fashion sense was decades ahead of the time. I doubt that the Seattle grunge rockers of the early 1990s were directly influenced by his shirts, but they could have been!