A farm administrator can do anything in your SharePoint environment! and he is a member in a group called farm administrator, so let’s see who are the members of this group in SP 2010. By default there are 3 members in this group which are as the following:
1- The user the you specified in the identity of the SharePoint central administration application pool, if you open your IIS manager, and go to application pools and see the application pool that runs the central administration, you will see the account the you specified while running the SharePoint configuration wizard. this account is part of the Farm Administrators Group.
2- The local Administrator of the server that has SharePoint installed in it. but one important note i like to add. if you have Domain Controller on your server and installed SharePoint, you will notice that the local administrators group is gone. you will not find this option in your windows settings when you have domain controller installed your server.
3- As you have guessed it. The user that you used when you installed SharePoint. This user for sure will be part of Farm Administrator.
I Hope that this little note has helped you understanding the Farm Administrator group that you have been seeing all the time in SharePoint Central Administration.