About Who is a Surety
Who can be a surety-- well, anybody can be a surety. In the older days, sureties were typically individuals, as a wealthy individual would provide surety on behalf of another. This would normally be a wealthier individual who would vouch for someone's character, such as a cattleman that would vouch for the banker.
In modern times, a surety is normally a large insurance company, like AIG or Zurich. These companies have divisions of their larger insurance company that serves as a surety. These divisions focus solely on surety bonds and have a history of default that they use to determine the risk with regard to a specific bond.