(written from a Production point of view)
Robert Albert Bloch (5 April 1917 – 23 September 1994; age 77) was a legendary American horror writer who is perhaps best known for writing the 1959 novel Psycho, which was adapted by Joseph Stefano one year later and filmed by Alfred Hitchcock (featuring John Anderson, Frank da Vinci, and Ted Knight). He penned numerous other novels, stories, screenplays, and teleplays, some set in the infamous Cthulhu setting created by horror master H. P. Lovecraft, with whom he was a frequent correspondent.
He penned three Star Trek: The Original Series episodes. All of these were based on short stories written by him previously. "What Are Little Girls Made Of?" came out from three of his stories, most notably "Queen of the Metal Men", "Catspaw" was loosely based on his 1957 story "Broomstick Ride", while "Wolf in the Fold" was adapted from the 1943 story "Yours Truly, Jack the Ripper", which was previously adapted to an episode of Thriller in 1961. Two of his episodes ("What Are Little Girls Made Of?" and "Catspaw") make mentions of the "Old Ones", a term frequently used by Lovecraft in his stories.
According to Herb Solow and Robert Justman, Bloch's script for "What Are Little Girls Made Of?" was in such a bad shape that Gene Roddenberry had to rewrite it during the filming of the episode, which resulted in the production going two days over schedule. (Inside Star Trek: The Real Story, p. 204)
Bloch got disillusioned with Star Trek at the end of the second season, mostly because of the change in management under the new Paramount regime, and never returned to write more episodes after "Wolf in the Fold". (These Are the Voyages: TOS Season Two) He described fellow Trek writer Harlan Ellison as "the only living organism I know whose natural habitat is hot water." 
- "Robert Bloch, The Subtle Horrors of 'Star Trek'", Randy & Jean-Marc Lofficier, Starlog, issue 113, December 1986, pp. 27-29