Which is why I mentioned Yusuf in my original comment as well. I always saw them very much so as the integral parts of the XB1 vision, as they were always the ones best versed in the development of policies and overarching vision.
It's... not at all like saying Kaz. Kaz would be analogous to Ballmer, which is a silly comparison.
Here's all I can find at the moment:
http://www.fastcompany.com/3013767/don-mattrick
http://business.financialpost.com/2...-play-to-control-living-room/?__lsa=c0f2-674f
He spear-headed acquisition of "TV" talent, while ramping down relation to streaming services. By the rest of the executives in the Xbox division, he is attributed with the discovery and push for Kinect. He is also described by Xbox execs as the one with the "ambitious vision". Not to mention the little excerpt about him leading the planning of the Xbox One.
He is very much at the center of the design philosophy for the Xbox One, but again, as I said before I also blame Yusuf (which is less founded, since I've never really researched him like Mattrick). Yusuf might actually just be a figure-head, since I'm not too familiar with his background.