I plan to finish this with Cayden, and post what I've written. I'm having an absolute riot with it. It's been extremely helpful for building up his 'voice'.

Toyhouse thread, by the creator (explains how to use it):
https://toyhou.se/~forums/207.character-discussion/786182.oc-builder-update-may-18th

The actual website:
https://ocbuilder.neocities.org/