(written from a Production point of view)
Described as "UNDER-RESEARCH OFFICER LARRY RIDDLE, mid-thirties, not handsome, the solid, reliable type," he was among the landing party that beamed down to the iron-silica planet where Lazarus was found. He was later placed on the bridge assisting Spock in giving an analysis of the cosmic wink.
After his return to the USS Enterprise, it was revealed that he was infatuated with "Chemoscientist" Charlene Masters, who did not exactly return his affection. Despite her rejections, Riddle was seemingly relentless in his pursuit of Masters, having later brought her a long-stemmed red rose "compliments of the biological lab," to her work station in engineering.
A relationship between Masters and Lazarus develops under Riddle's nose. Riddle was absent from the remainder of the episode, and would finally appear in the last scene, after Lazarus was dispatched, when Kirk suggests to him that "Miss Masters is in sickbay... I think she might like some company," to which he obliged.
A later, undated final draft of the episode remains true to the first draft, however, by the revised final draft, dated 11 November 1966, all references Riddle as well as the relationship between Masters and Lazarus were completely removed. Riddle's name, however, did still appear in the "cast" portion of the script.