A diabetes specialist is called an endocrinologist. Endocrinologists specialize in the glands of the endocrine (hormone) system. The pancreas is the gland involved in diabetes. The pancreas produces insulin, and problems with insulin are what managing your diabetes is about.
Endocrinologists diagnose, treat and manage disorders of the endocrine glands - adrenals, pancreas, pituitary, parathyroid, thyroid, ovaries and testis - and their associated hormones. Diabetologists are endocrinologists who specialise and focus on the treatment of diabetes mellitus