I've inherited control of an AWS MySQL RDS instance. I'm curious to know what the 'rdsadmin' user is and whether I should know the password for this or whether this is purely for use by the Amazon Web Console.
This is Amazon's own user that is used by Amazon to perform updates, run backups and do other maintenance tasks. That said, Amazon's support should be able to advise you.
In general, you don't need to (and should not) know the password.