(written from a Production point of view)
Allen was born as Alan Cohen in Cleveland, Ohio. He graduated with a Bachelor's Degree of Fine Arts in Theater at UCLA in 1954, and worked mainly as an actor afterward. He was often cast in the role of brash, arrogant young tough guys, most notably as Buzz Gunderson in Rebel Without a Cause (with Ian Wolfe, Chuck Hicks, cinematography by Ernest Haller and music by Leonard Rosenman). On stage, he appeared in an Equity production of My Three Angels, directed by future Star Trek director Ralph Senensky.
Meanwhile, Allen directed a number of theater plays, including many Equity productions in Los Angeles. This lead to his long directing career, mostly in television. During his thirty years as a director, he helmed episodes of dozens of television series, including The Streets of San Francisco, Barnaby Jones (starring Lee Meriwether), Hill Street Blues (which he won an Emmy Award directing an episode for), T.J. Hooker (starring William Shatner, James Darren, and Richard Herd), Dallas (featuring Susan Howard and Joshua Harris), Murder, She Wrote (featuring William Windom) and Magnum P.I.
His association with Star Trek began with directing the pilot episode of Star Trek: The Next Generation, "Encounter at Farpoint". In the next seven years, Allen continued to work on The Next Generation and Star Trek: Deep Space Nine. He had a tendency to direct scenes in a very fast pace, which often resulted in his episodes being too short. During the filming of "Encounter at Farpoint", Gene Roddenberry wrote additional scenes in order to fill the ninety-minute length of the pilot. He was interviewed by Edward Gross for the article "Corey Allen – Directing Farpoint Encounters", published in The Official Star Trek: The Next Generation Magazine issue 10, pp. 62-66. In this interview, he cited the science fiction pilot that he directed shortly before "Encounter at Farpoint", The Infiltrator, as his training ground.