serveradmin
Members of the serveradmin fixed server role can change server-wide configuration options and shut down the server.
See Also
Reference
Concepts
Permissions of Fixed Server Roles
Other Resources
sp_helpsrvrole (Transact-SQL)
sp_helpsrvrolemember (Transact-SQL)
sp_srvrolepermission (Transact-SQL)
Security Considerations for Databases and Database Applications