One fine day in a tranquil land made of cardboard, an eccentric and demented scientist was plotting. He'd decided that life was just too tedious and one-dimensional for him, so he built himself a monster-making machine.
This grand device churned out a stack of 2D templates, slots were cut and within no time these ferocious flat-packed freaks began to fit themselves together. The scientist then gathered the finest artists in the realm to decorate these free-standing fiends, leaving a few of them blank so that the local villagers could make them their own.
Naturally he wanted to share his colourful creations and enrich the whole kingdom so he constructed a series of large envelopes which allowed him to post them to the farthest reaching corners of the land. What a lovely chap.