Zen is the work of a huge team of talented engineers. To single one out as "the man behind Zen" seems very wrong. I don't know what Jim Keller's contribution to Zen was (and without a blog or autobiography or similar from someone well placed inside the team, then neither do most commentators), but if he did work on the Zen architecture, it's hard to believe that he would have accomplished much without the help of a good team. Keller is the main AMD engineer singled out for praise on The Internet, while the hard work (and given that Zen is such a success, it's surely the result of a mountain of hard work) of everyone else is mostly ignored.