Ask any Marine - they remember their Drill Instructors for the rest of their lives.
These Marines will mold you for 13 weeks, forever changing you from you were when you arrived into a United States Marines.
CHIEF DRILL INSTRUCTORS
The Chief Drill Instructor is the senior ranking Drill Instructor in each series. They are the enlisted advisor to the Series Commander, reporting to him on the progress of the platoons.
They are responsible for all recruits and drill instructors in the 3 platoons assigned to them. There are two Chief Drill Instructors per company - one for Lead Series, and one for Follow Series.
A Chief Drill Instructor is highly experienced in recruit training. They are usually Staff Sergeants or Gunnery Sergeants.
You do not want to be noticed by your Chief Drill Instructor. Sitting outside their office usually indicates you will be awaiting punishment. Stay out of their way.
THE SENIOR DRILL INSTRUCTOR
Recognizable by their black Ceremonial Belt, the Senior Drill Instructor leads the platoon of recruits.
From delivering the "Black Friday" Speech to leading the platoon in Initial and Final Drill, the DI oversees every aspect of training. The other drill instructors in the platoon report to the SDI.
Your SDI is usually a Staff Sergeant or Gunnery Sergeant. Occasionally they will be a Sergeant, indicating a Marine who has demonstrated exceptional leadership and training ability.
SDI's have years of recruit training experience and are proficient in making Marines. They act as leaders and mentors, looking out for your development, personal progression, and well-being.
Green Belt Drill Instructors (DIs) are the remaining 2 - 4 DIs per platoon that train Marines.
They vary in rank from Sergeant to Gunnery Sergeant.
Green Belt DIs are responsible for executing the actual training, instilling discipline in recruits, and do most of the yelling DIs are famous for. Green Belts have an unnatural ability to spot undisciplined recruits who move, scratch, itch, or breathe when they are not supposed to.
Green Belt's will lead most Incentive Training (IT).
The most senior of the DIs (besides the SDI) is sometime referred to as the Experienced DI (EDI) or "Heavy." This unofficial term indicates the SDIs right-hand and most reliable DI who will lead most of the platoon's training when the SDI is not around.