What is the user postgres wants a password for?

What is the user postgres wants a password for?

I'm at such a loss-- I did a fresh install of Postgres (Windows 7) and I
still can't do anything.
When I try to run any command, even psql -l, it asks me for a password,
then tells me password authentication failed for user Aerovistae.....WHERE
IS IT GETTING THESE CREDENTIALS FROM? What password does it want??
When the program was set up it only asked me to supply info for the
postgres superuser, which I did...where is it getting the user Aerovistae
from, which is my normal handle but not one I supplied to postgres! I'm so
confused.