Martyn Russell is Tracker's release manager, and being a fan of the project since the early pre-1.0 days, I have quite familiar with his work. But what triggered this honor is his work on Tracker Needle (written in Vala), Tracker's new GUI search tool, to replace the inadequate Tracker Search Tool (written in C). I've taken a look, and the design is pretty modern (check the video he gives in his announcement).
But Martyn has of course done far more for Tracker, and does a pretty damn good job managing the release. One thing he did outside of Tracker that I'm aware of is the re-design the http://gtk.org page, giving it a very modern look (which it desperately needed).