Mr. Freeze was initially just another Batman villain with a "gimmick", and had in fact been killed off in a storyline in the Batman comics at the time Batman: The Animated Series (1992) debuted on television. Not long afterwards, the comics resurrected the character and incorporated the tragic backstory Paul Dini had created for him.
Bruce Timm came up with the idea that Freeze barely escaped dying in a cryogenic experiment gone wrong, and considers himself dead. As a result, he doesn't fear death and has no emotions.
Bruce Timm noted he had difficulty getting Michael Ansara to play it "flat" for the role of Freeze. "He was acting too much. It was really frustrating for him. He had never done cartoons before and an actor's first natural instinct is to act. He kept giving these line readings with all this inflection in them. I kept telling them that it had to be less, a lot less- like a robot. He kept saying it sounded so flat. Everybody else was looking at me too, and was asking me if I was sure. To them it sounded flat. I think it really sells it. I wanted his voice to sound like the Ebonites in that old The Outer Limits (1963) episode: 'Nightmare.' They sound real metallic and hollow. I even played that for him at the recording session, and explained that was what I wanted it to sound like. It drove the sound guys crazy doing it."