Corin Nander recalls the Gundam from his past—it's the Wing Zero! Director Tomino wasn't very familiar with Gundam Wing so he didn't initially realize that it was added in by staff, but he's happy with the end result. It fit the thematic framework of encompassing all Gundams.
I've tweeted about this before, but here's a refresher thread.
The original internal working title of Turn A Gundam was "Ring of Gundam". Tomino wanted to deliver a story that would expose the origin of humanity's sin, and in doing so he aimed for a "restoration" of Gundam.