Mark Piper Dr . Mark Piper was a male Human Starfleet officer who lived during the mid - 23rd century . He served in the sciences division aboard the 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 . In the latter capacity , Piper was present on the bridge when the " Enterprise " crew embarked on an exploratory expedition outside of the Milky Way Galaxy . He also introduced the recently posted Doctor Elizabeth Dehner to the captain . After the ship ' s encounter with an exotic energy field at the galaxy ' s edge , Piper tended to lieutenant commander Gary Mitchell and Dr . Dehner , who were mysteriously affected by the barrier . Later , Piper accompanied Captain Kirk and a landing party to the surface of Delta Vega , where the crew was attempting to adapt the power pack s of an automated lithium cracking station to regenerate the ship ' s warp engine s . While there , Piper observed Lieutenant Mitchell , who had begun to manifest extremely powerful psychokinetic abilities as a result of his exposure to the energy barrier . Along with the rest of the landing party , Piper was knocked unconscious by Mitchell as he escaped with Dehner . After regaining consciousness , he revived Captain Kirk , who ordered the doctor not to revive Spock until after he had departed after Mitchell . Kirk further ordered Piper that should Kirk not report back within twelve hour s , the " Enterprise " was to travel to the nearest Earth base at maximum warp with Kirk ' s recommendation that the entire planet be subjected to a lethal dose of neutron radiation . ( ) Appendices . Background information . Piper was played by Paul Fix . The first draft of the script simply described him as the " Ship ' s Doctor " throughout , but was at one point addressed by Kirk as " Dr . Johnson " . The uniform Piper wore had one braid indicating an officer rank less than captain . After the departure of John Hoyt ( Philip Boyce in ) , 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 . ( " " , p . 75 ) 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 . ( " The Star Trek Interview Book " , p . 118 ) Ultimately , Gene Roddenberry was unsatisfied with the way Paul Fix portrayed the character , and believed something was missing from the role . ( " " , p . 84 ) D . C . Fontana explained , " " Gene wanted a somewhat younger , more active doctor . He didn ' t want an aging , he wanted definitely a younger , more vigorous doctor . " " ( " Starfleet Access " for " Where No Man Has Gone Before " , TOS Season 1 Blu - ray special features ) Writer Samuel A . Peeples was also unhappy about how Paul Fix played the doctor , later remarking , " " In my opinion he was a little too old for the part [ . . . ] I just felt he wasn ' t right for the part . " " This was despite the fact that Peeples found Fix to have done " a good job " of playing the old country doctor that Piper was meant to be . In other words , Peeples felt the problem was more in how the character had been conceived . He went on to say , " " The physical element , I thought , required every crewman of the USS " Enterprise " to be active . He had to be not only mentally alert , but the traditional images of a country doctor would hardly have fit the images of a man who would say , ' We ' ve got an unknown disease , and there ' s a cure on this planet . Our only choice is to try it . It might kill you , ' and I don ' t think Paul Fix ' s interpretation of the character would have been able to do that . " " In conclusion , Peeples agreed with interviewer Allan Asherman ' s assessment that Fix , in the role , was " distinctly twentieth century . " ( " The Star Trek Interview Book " , p . 118 ) Due to Gene Roddenberry ' s dissatisfaction with the part , the character of Mark Piper was replaced – as regular doctor – by Leonard McCoy ( played by DeForest Kelley , who Roddenberry had been wanting to cast in the position since working on " The Cage " ) . ( " " , pp . 75 & 84 ) NBC ' s early - 1966 series sales booklet ( which was made when Piper was still considered to be a regular ) gave this biography of the character ( reprinted in " " ) : Apocrypha . The character of Dr . Mark Piper also appeared in the novels " Captain ' s Peril " by William Shatner , " et al . " and " " : " Harbinger " by David Mack . " Captain ' s Peril " mentioned that as an infant , Piper was " bounced on the knee " of Jack Archer , presumably a relative of former Captain Jonathan Archer , if not the Captain himself . In the novel " " , as Kirk assumed command of the ship for the first time from Captain Pike , Piper had been replaced by McCoy . However , McCoy was late reporting in from leave and Kirk tried to contact Piper to fill in , but couldn ' t reach him , either . McCoy finally reached a location with communications and reported in . In the subsequent novel " Strangers from the Sky " , McCoy went on leave to deal with " personal matters " ( his divorce ) , and Piper filled in temporarily , pending his retirement from Starfleet . Thus , Piper was aboard when the " Enterprise " explored the edge of the galaxy . In the novel " Traitor Winds " ( set sometime between TOS and ) , Piper was killed by traitors within Starfleet . " " incorrectly gives his first name as Paul .