When looking at the Revision History of a user in CA Agile Central, there are changes that show the Author as System User.
The System User is internal to the CA Agile Central SaaS infrastructure. It is an automated service account used to disable users after the Maximum Failed Login Attempts setting has been reached. It and also to enables users after the Amount of Time Users will be Locked Out period has expired. These are settings set by the internal Subscription Administrator.