I faced some headache installing PostgreSQL on my Mac via Homebrew (a package manager for MacOS kinda like apt-get for linux). After installed, I tried to use its console and:
1 PostgreSQL error: Fatal: role “username” does not exist
After wander around the web and some StackOverflow questions later, I solved the problem by running in the console:
The problem was that Postgres was looking for the default database which is named after your user name.
createdb without any arguments, does the trick by creating a database with your user name.