Username for Controller

[eluser]Unknown[/eluser]
Hello,

I'm trying to figure out how some sites display a username for their profile page (e.g. http://www.foobar.com/johndoe). Would you just define a controller and all the actions for the profile and simply when a new user is added their username become a controller that extends your profile controller?

I'm sure it's a simple question, but it perplexes me at the moment.

Thanks,
Ben