How do you recover you RDS master user username?

The master user name can be recovered with the rds-describe-db-instances command.

If you are using aws cli-2, command shall become :

aws rds describe-db-instances --region ap-south-1

The master username is now listed in the RDS Dashboard.

1. Select the "Instances" listing and expand the DB instance.
2. Press the looking glass tab on the left.
3. The master username is listed in the left column.

Hope this helps!

It is 2019 now. It is 'Databases' on the sidebar, 'Configuration' on the navigation bar. And look for username.

With the new updated RDS UI, the username is present in the Details section of the Instance Information screen.

1. From the List of your running Instances, click an instance name to see information about the instance.
2. See the "Details" section of the information screen.

scroll down in that screen to see the "Details" section.