Create a "postgres" user account on OSX?

I just made a mistake: I installed PostgreSQL on Mac OSX 10.6.7 and when I wanted to connect to it I did su postgres, then it asked me for a password and I did sudo passwd postgres to change the password to something I know.

The problem is, as explained here, this created a Unix user account for postgres and afterwards I had two users on my Mac : me and postgres.

So I deleted the postgres account. Now I cannot connect to postgres because I just cannot su postgres. How to recreate a "locked" user account postgres that I could use safely (by doing sudo su postgres as I should have done before) ?

Edit: added version of Mac OS X

Solution 1:

from the following stack overflow:

https://stackoverflow.com/questions/15301826/psql-fatal-role-postgres-does-not-exist

CREATE USER postgres SUPERUSER;
CREATE DATABASE postgres WITH OWNER postgres;