The term "Master Chief" primarily refers to a senior enlisted rank in the United States Navy and Coast Guard, known as a master chief petty officer. These highly experienced individuals often specialize in diverse fields, such as Master Chief Musician or Master Chief Hospital Corpsman. Beyond these general rates, "Master Chief" also designates the unique, top enlisted positions: the Master Chief Petty Officer of the Navy (MCPON) and the Master Chief Petty Officer of the Coast Guard (MCPOCG), who serve as senior advisors. Interestingly, the name has also achieved significant pop culture fame as the iconic protagonist, Master Chief Petty Officer John-117, from the popular Halo video game series.