As it turns out, the area's fairly well-known as "Mullae Art Street", and there's even a rough map of it made out of lug nuts posted at what I guess is the entry point:
Street art and graffiti are uncommon and generally of poor quality in Korea, with the Hongik University area in central Seoul being the only place you really see it, with the exception of the occasional poorly-done mural for children near a school or park.
This area is largely a derelict commercial-industrial zone, full of metalworking and repair shops, many of which are abandoned now. One day, I guess someone who worked at one of these shops decided to make a creative sign or sculpture, and it set off a chain reaction.
I don't imagine the area will be around much longer, what with the rapid development that characterises Seoul and the ever-increasing property values that accompany it. Gentrification, basically. That's always the next step after artists start flocking to a crappy downtown area and make it cool, right?
Robo-Heisenberg was easily one of the best things, if not the best. See him in action in the video at the bottom of the post.
I'm not sure what kind of social commentary this angry kid with a shrimp earring, fish necklace and two different shoes is, but I like it.