One who practices chiropractic. According to the American Chiropractic Association, a chiropractor "provides conservative management of neuromusculoskeletal disorders and related functional clinical conditions including, but not limited to, back pain, neck pain and headaches."
Many chiropractors believe that spinal subluxations cause spinal and neuromuscular problems ranging from TMJ to migranes. Just as many eschew the idea that subluxations and nerve interference are the underlying cause of disease and concentrate only on musculoskeletal corrections. (I think most chiropractors would agree that spinal injuries do not cause diseases such as cancer or heart disease.)
Chiropractors provide spinal and other manipulations and adjustments to both relieve pain and keep the spine from degenerating at a faster rate than is normal. There is a scientific basis to chiropractic, though the success of its claims is widely debated. Still, licensed chiropractors must graduate from an accredited chiropractic school. The field continually conducts scientific research and updates its standards and practices.
References and sites of related interest:
American Chiropractic Association: http://www.amerchiro.org
Canadian Chiropractic Association: HTTP://WWW.CCACHIRO.ORG
Chirobase: http://www.chirobase.org/13RD/chiroguidelines.html.