In the beginning, after you create your Vanilla Forum, there will be two accounts. One account is your super admin account, the other account is your system account. The system account does automated tasks. For example, when you use Vanilla's Comment System on your blog, discussions in the forum will be added automatically by this system account.
Modifying the look
The system account, out of the box, has the Vanilla Forum logo and the name "System". To change the default look, login to the forum as as Admin, then navigate to the system profile and click "edit profile". Below is example of the screen where you can change the name:
If you are looking to change the default image, click "change picture" on the edit profile menu:
Now you are able to have your automated account a little more customized to your site.