A rheumatologist is a specialist doctor who first has to complete their Bachelor of Medicine and Bachelor of Surgery, then has to train further for another 4 years to become a specialist physician (internist) which involves training in all the various disciplines of internal medicine (lungs, heart, kidneys, brain, endocrine and ICU).
After becoming a specialist physician, they have to train further in depth in the field of rheumatology (diseases of the joints, muscle, bone, but many of these rheumatological autoimmune diseases can also infiltrate the organs, not only the joints eg. lungs, heart, eyes, mouth, kidneys, brain, bowel and skin). The rheumatologist has to monitor all these organs for disease, and whilst the patient is on treatment. Many of these diseases are chronic / long term / life long.