I think Ryu Hayabusa fits the title of badass perfectly.

Especially in Ninja Gaiden II.
And yes, NGII is hard...in fact, I'd say it's harder than the one for the X-Box. However, it does have an easy mode available and while the bosses are still pretty tough, some of the normal enemies seem a bit easier. Well, at least until the fifth chapter.
It's a tough game. However, it's supposed to be and that's what I love about the series.