The last time Nintendo had a completely new, built-from-the-ground-up console GPU (not merely semi-custom work based on a PC GPU) was the Flipper for Project Dolphin (GameCube).
Even the Wii U's Latte GPU was pretty much a semi-custom lower-end RV7xx with 32 MB EDRAM. -- And the Wii's GPU was just an overclocked Flipper.
Anyway, Flipper was designed by ArtX from about 1998 to 2000. It wasn't based on any Radeon design because there were no Radeon GPUs back in 1998-1999. ArtX had made a PC GPU for Acer and showed it at Comdex 1999 but this didn't go anywhere.
Everything ArtX did went into Flipper for Nintendo. There wasn't anything like it before or after, not counting the Wii's overclocked version (named "Hollywood").
http://www.eetimes.com/document.asp?doc_id=1145794