Who is the "IIS general Windows User Account" to access Asp.net/SQL?

Hi Folks,

I want to clarify some things regarding "SQL Security & Network Connectivity" and how it relates to memberships.

Q#1
Who is the IIS general "Windows User Account"?
For Asp.net web site, it appears that IIS uses a single "Windows user account as a gateway to connect "all the members of the website?" to the SQL Server....?
What permission, does this user have by default?

Is it a SysAdmin, a DBOwner, what?
Can I change the "roles" of this "Mr.Everybody" User Account?

What I would like to do (if you concur it as being a good idea) is to have one "Windows User" for all Web-traffic with limited permissions
and another "Windows User" for an admin to connect from SQL Studio Manager with more permissions�

So, if for any reason there are SQL injection attacks via the Website interface, in any case, the "Mr.Everbody" acc ...