The Security Chief is an administrator in charge of your prison's security forces. He unlocks Deployment, Intelligence, and Surveillance research.
Once assigned to an office, he will give you a real-time report of the prison's danger level, and tells you how many prisoners have lodged complaints, and how many are pacified.
You can only hire one chief, and as a pure administrative staff he won't act as a guard e.g. by escorting prisoners or opening jail doors.
The Security Chief will lead the Tazer Certification program for guards in the classroom. He also attends executions.