(written from a Production point of view)
Cronenberg was approached for the role by showrunner Alex Kurtzman, who's a fan of his work. He said he was also "cheap and (as a Toronto native) available". As a fan of Star Trek: The Original Series, Cronenberg was delighted to be offered a part on the franchise. 
Considered to be an auteur of the horror genre, and pioneer of the "body horror" subgenre, Cronenberg's body of work includes films such as The Brood (1979, starring Samantha Eggar and featuring Felix Silla), Scanners (1981), Videodrome (1983), The Dead Zone (1983, with Anthony Zerbe and Helene Udy), The Fly (1986), Dead Ringers (1988, starring Geneviève Bujold), Naked Lunch (1991, starring Peter Weller), Crash (1996), eXistenZ (1999), and A History of Violence (2005, with Stephen McHattie).
As an actor he has also had cameo roles in a number of his own films, as well as appearing in films such as To Die For (1995, with Kurtwood Smith and Conrad Coates), Extreme Measures (1996, with Paul Guilfoyle and Tara Rosling), and Jason X (2001), and TV series like Alias (with Greg Grunberg, Melissa George, and Merrin Dungey, created by J.J. Abrams, executive produced by Abrams, Roberto Orci and Alex Kurtzman) and Alias Grace (with Jonathan Koensgen and Ana Shepherd).
Star Trek appearances