I thought abotu leo_draconis, but the earliest fic I can find for her was 2008...

There's also naadi, who was writing fic as early as 2002 I believe? and creating stories through art up to last year (although I believe she's announced she's no longer going to create for fandom?) So I'm not sure how she fits in this due to the fact that she's an artist and may have officially left fandom as of 2015...

I'm guessing that artists would qualify for a separate list :)