In the early days and all through my year long involvement it was code named "Project Y".
Why? I don't know.
I created a massive amount of conceptual work for Naughty Dog. In the beginning they shared the images with Sony Japan for their input. Sony liked this design for the central character and wanted to go in this direction initially.
ND didn't agree and stopped showing things to Sony Japan soon after but for a while I was continuing along this path and gradually got closer to what would become the central character of Jak. Here are a few more samples of what I was experimenting with at the time.