The endocrine system is the part of the body that produces hormones which act on the rest of the body. An endocrinologist, therefore, studies that system and the hormones it produces.
A doctor.
There are various types of Specialists in Medicine. They have various titles depending upon the Speciality they work viz General Physician, General Surgeon, Chest or Respiratory Physician, Cardiologist, Gastroenterologist, Neuro Physician / Surgeon, Paediatrician, Gynaecologist & obstetrician, Nephrologist, Urologist, Endrocrinologist, Pathologist, Radiologist, Radiotherapist, Orthopaedic Surgeon etc.........