Yes, Mathieson, along with Martin Brennan and Ben Cheese had all worked at Sinclair on the Loki project just before the Amstrad buyout. They then left and formed Flare Technologies and designed the Flare 1 chipset in the mid 80s (I think the first production ready chips appeared around 1987). They were then commissioned to modified that design into the hardware for the Konix Multisystem, which led to the Slipstream ASIC (slightly enhanced single-chip Flare 1) in 1988. They left Konix in early 1989 and split up, doing various consult work at that point.
In '89 Martin Brennan was commissioned by Atari to complete the Panther video processor design, which then led to him suggesting Atari invest in a more advanced design which became Flare 2 and eventually the Jaguar. (headed by Brennan and Maitheson -Cheese didn't work on the Jaguar) Meanwhile, Ben Cheese ended up working with Argonaut and contributed heavily to the MARIO chip (Super FX) design.
Then Mathieson and Brennan worked on the Jaguar II (midsummer) chipset before leaving Atari in '96 and again splitting up.
Beyond that, Mathieson worked on the Nuon project and eventually joined Nvidia as mentioned.
More info on the Flare 1 and Konix stuff here:
http://www.konixmultisystem.co.uk/ (the interviews in particular are interesting)
The Nvidia Project Shield is currently in development and is plans for a new console/handheld design using the Tegra 4 processor:
http://en.wikipedia.org/wiki/Nvidia_Shield
It's supposed to be released in the middle of this year. (was announced at the winter CES this January, and I assume will have a more solidified showing at E3) Wiki actually lists it as being planned for a Q2 2013 release, but the 2nd US fiscal quarter ends in March, so I don't see that happening. :p