Why is my dad coughing violently?

My dad keeps coughing violently throughout the day, and has been smoking for as long as I can remember. He is very headstrong and will not go to the doctors, despite me telling him to. He acts like he's fine, but it's obvious that he's not. He hasn't been coughing up blood or anything like that, as far as I know. He did drink a lot of coffee, and that made him cough a bit, but not a lot compared to now. He hasn't drunk coffee in months, but the problem persists. Why is he coughing so violently?