I worked with an software developer at my last job who was incredible. He seemed to have a strong interest for the technology, no matter what technology that was. At the time, it was iOS, and he was an absolute master of iOS. I was constantly impressed by his attention to detail and emphasis on quality, well written, technically challenging code.
I've loosely followed him since, and he seems to be absolutely crushing it wherever he goes. He's spanned many different roles and seems to do enjoy taking on new challenges in the form of different programming languages / platforms.
When I think back to him, I remember someone who seemed to just love programming. In a way, he was like a Robot. It doesn't appear to matter much to him what he's working on, or if it's "fulfilling" in the ethical sense.... He just enjoys the process of coding, and being damn good at it.