Luka was formerly known as Dr. Luke Caldwell and one day, he was working a chemical cure for cancer and he tested it on himself. However, this chemical mixture caused him to mutate into a lizard humanoid like creature that was incredibly violent, so he killed everyone in the lab. When he woke up from his mindless fury, he went into hiding in the Nevada desert until he could be able to control his new abilities. For his voice, he would have a medium, normal sounding voice, but when he is in a fury, he should have a deep, monstrous sounding voice. Here's his theme to give you better idea of his story and personality: https://youtu.be/5mwEemWkZFo