In particular the Watch sub-series.

I grew up reading them from the late 80's on-wards and I actually can't separate my worldview from them anymore, his outlook on life became my outlook on life.

Hope, Cynicism, politics, mortality (Death is a literal character), practicality and absurdity all feature in the series strongly.

Some of my favourite quotes

> Logic is a wonderful thing but doesn't always beat actual thought. (The Last Continent).

> Genius is always allowed some leeway, once the hammer has been pried from its hands and the blood has been cleaned up. (Thief of Time).

> I believe in freedom, Mr. Lipwig. Not many people do, although they will, of course, protest otherwise. And no practical definition of freedom would be complete without the freedom to take the consequences. Indeed, it is the freedom upon which all the others are based. (Lord Vetinari - Going Postal).

> What sort of man would put a known criminal in charge of a major branch of government? Apart from, say, the average voter.

> Technically, the city of Ankh-Morpork is a Tyranny, which is not always the same thing as a monarchy, and in fact even the post of Tyrant has been somewhat redefined by the incumbent, Lord Vetinari, as the only form of democracy that works. Everyone is entitled to vote, unless disqualified by reason of age or not being Lord Vetinari. And yet it does work. This has annoyed a number of people who feel, somehow, that it should not, and who want a monarch instead, thus replacing a man who has achieved his position by cunning, a deep understanding of the realities of the human psyche, breathtaking diplomacy, a certain prowess with the stiletto dagger, and, all agree, a mind like a perfectly balanced circular saw, with a man who has got there by being born… A third proposition, that the city be governed by a choice of respectable members of the community who would promise not to give themselves airs or betray the public trust at every turn, was instantly the subject of music-hall jokes all over the city.