Leonard H. McCoy, MD, was a noted Human physician and scientist of the 23rd and 24th centuries who served as ship's surgeon and chief medical officer aboard the Federation starships USS Enterprise and USS Enterprise-A for 27 years.
McCoy was an accomplished surgeon, xenophysician, exobiologist, and an expert in the field of space psychology. Born in the "Old South" region of North America on Earth, in 2227, McCoy was commissioned to Starfleet in the 2250s. In his early career he made numerous medical advancements in virology and neurology before being promoted to lieutenant commander.
He joined the USS Enterprise, under command of James T. Kirk in 2266, replacing the outgoing Dr. Mark Piper as chief medical officer and ship's surgeon. During his posting, Kirk liberally used the nickname, "Bones" (short for "sawbones", the ancient description of a surgeon) for McCoy and the name stuck for the remainder of their friendship.