This is definitely a sad day for everyone in my generation who grew up with the Harry Potter films, as well as those who were fortunate enough to witness him perform live as I was.
Hans Gruber is the definitive Alan Rickman role for me (I haven't seen the Harry Potter films because I didn't enjoy the first book and didn't read any of the later ones). He's just about the perfect "baddie", with his blend of urbane rationality and vicious ruthlessness. Also, in his final death-scene, Rickman had to fall
twenty-one metres onto a green-screen landing pad. No stunt-double. That's pretty badass if you ask me.
Edit: Fixed grammar mistake.