The Captain is the Captain because he’s the Captain.
Stupid passengers.
Under U.S. FAA FAR 91.3, "Responsibility and authority of the pilot in command", the FAA declares:[4]
The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.
In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule of this part to the extent required to meet that emergency.
Each pilot in command who deviates from a rule under paragraph (b) of this section shall, upon the request of the Administrator, send a written report of that deviation to the Administrator.