(written from a Production point of view)
Robert "Bob" Butler (born 17 November 1927; age 86) directed the original series' first pilot episode, "The Cage". Butler was born in Hollywood, Los Angeles, California from Irish Catholic parents.  He has built a long career in television, directing episodes of over 90 television series, notably The Twilight Zone (including "The Encounter" starring George Takei), Hogan's Heroes, The Fugitive, Batman (including two episodes guest-starring Frank Gorshin as The Riddler), Gunsmoke and Remington Steele. Butler seems to have made something of a specialty of directing the pilots of hugely successful series. Not only did he shoot the first ever Star Trek episode but he also directed the pilots of Lois & Clark (starring Teri Hatcher), Moonlighting (with cinematography by Jerry Finnerman), and Hill Street Blues (starring James B. Sikking).
Butler was chosen by Gene Roddenberry to work on the first pilot for Star Trek after he has directed some episodes of Roddenberry's previous series, The Lieutenant (starring Gary Lockwood). However Butler was quite dissatisfied with Roddenberry's production decisions and the show itself, so he declined to direct more episodes (including TOS: "The Menagerie, Part I" and TOS: "The Menagerie, Part II"). He called the series "too square-jawed, heroic" for his taste, and opted for something more like The Twilight Zone.