Harry was originally intended to be more serious like his comic book counterpart, but Alan Tudyk was so dazzling in his audition that the character was reimagined to suit his comedic talents.
In the comics, Harry was addicted to old pulp detective novels. In the show, it was switched to Law & Order (1990) reruns.
Deputy Liv was only intended to be a small recurring character, but Elizabeth Bowen had such an immense rapport with Corey Reynolds (Sheriff Mike) that they expanded her role.
The alien makeup is comprised of a large helmet-like mask that fits over top of Alan Tudyk's head, with smaller prosthetics covering his mouth and nose, plus a set of fake teeth and hands. Tudyk's transformation into Alien Harry generally takes two hours. The blinks and eye movements are created digitally in post-production.
Corey Reynolds suggested to creator Chris Sheridan that his character should have a quirk, like beatboxing. Reynolds proceeded to demonstrate while simultaneously humming "Amazing Grace," and he was soon accompanied by Elizabeth Bowen, who joined in on mouth-trumpet. Sheridan was wowed and exclaimed, "That's going in the show!"