I heard late last night about William P. Alston's death earlier in the day, strangely not through any departmental channels but through a friend who never met him. He was one of the professors I've most respected in my entire academic career. He wrote his dissertation with Wilfred Sellars on the work of Alfred North Whitehead but spent most of his career on philosophy of language, philosophy of religion, and epistemology. Along with Alvin Goldman and Alvin Plantinga, he helped spearhead the externalist/reliabilist revolution in epistemology, a tradition that I think took things in the right direction. He also was one of the most important figures in the revival of philosophy of religion in the last four decades from a point where it had become looked upon as a joke except to reject traditional religious views to a point where some of the most important philosophers today are Christians or other theists. Alston himself was not a Christian when he began his philosophical career, a path shared with several other notable Christian philosophers (Norman Kretzmann and Peter van Inwagen come to mind).
It was always encouraging to me to think about how successful he was in philosophy given his personality and philosophical temperament, which I think are similar to mine in a number of ways that I'm not like most of my philosophical colleagues. He wasn't a system-builder. He wrote about what he had something to say about but wasn't trying to put together a comprehensive philosophical view on every issue he could have something to say about.
Most of his work didn't involve coming up with brilliant views on cutting-edge issues that no one had ever thought of before (although I think there are a few occasions of that in his work, especially in his most recent work in epistemology). He tended to favor traditional views, sometimes so traditional that the majority in philosophy had left the view so far behind that they considered it a joke until people like him came along to disabuse them of such notions by defending the views in novel ways.
Some of the most important philosophical figures are noteworthy for one or both of those reasons (system-building and novel views). Alston, however, filled a role of simply doing good philosophy, often in small but important details. He might see a fallacious argument that was nonetheless popular and apply an important distinction, perhaps one known to the medievals but often ignored by contemporary philosophers, to show why the argument fails. He found elements of competing views that might be compatible and explained why a moderating position might be better than either original view. He applied new arguments in epistemology, philosophy of language, philosophy of mind, or metaphysics to some problem in philosophy of religion to show why a new trend in a completely different area makes Christian belief more favorable (e.g. his application of functionalism, a recent view in materialist philosophy of mind, to explain how language about God can be literally true even if not used in exactly the same sense as the same terms are used for us).