Dan Robbins was no Leonardo da Vinci. But he copied one of the master’s basic techniques and thereby enabled children to grow up believing that they, too, could paint “The Last Supper.”

Mr. Robbins, a package designer who died on Monday at 93, helped to conceive what became known as paint by numbers. He copied the idea from Leonardo, who numbered the objects in the background of his paintings and had his apprentices paint them with designated colors.

With paint-by-numbers kits, young baby boomers in the 1950s followed the same mechanics as those Renaissance artisans, coloring inside the outlines of images of everything from seascapes and the Matterhorn to kittens and Queen Elizabeth II. The process opened up art to the masses — another notch on the continuum of a limitless democratic American ethos that promised “a chicken in every pot” and “every man a king.”

As the packaging on one paint-by-numbers kit promised, “Every man a Rembrandt.”

For a time, it might be said that Dan Robbins, who was essentially an illustrator, was the most exhibited artist in the world. His original freehand drawings provided the templates for the paint-by-numbers kits, and the results covered the empty walls of newly built postwar suburban living rooms.