Who was Dr. Leonard McCoy's predecessor on the USS Enterprise in the original series of "Star Trek"?

Dr. Mark Piper was a male Human Starfleet officer who lived during the mid-23rd century. He served in the sciences division aboard the USS Enterprise under Captain James T. Kirk, during his historic five-year mission. In 2265, Piper served as both the ship's chief medical officer and life sciences department head. ("Where No Man Has Gone Before.")

Piper was played by Paul Fix, however the first draft of the script simply referred to him as the Ship's Doctor throughout. Mark Piper was temporarily intended to fill the vacancy of Star Trek's regular doctor character. A casting recommendation from Director James Goldstone to Gene Roddenberry led to Paul Fix being cast as Piper.

The fact that Roddenberry, Goldstone and Casting Director Joseph D'Agosta discussed the regular doctor as being an old country doctor was a deciding factor in the casting of Paul Fix.

Ultimately, Gene Roddenberry was unsatisfied with the way Paul Fix portrayed the character, and believed something was missing from the role, and the character of Mark Piper was replaced by Leonard McCoy (played by DeForest Kelley, who Roddenberry had been wanting to cast in the position since working on "The Cage").