I was reading Neil Gaiman's eulogy for Terry Pratchett. This part stood out to me:
Terry looked at me. He said: "Do not underestimate this anger. This anger was the engine that powered Good Omens." I thought of the driven way that Terry wrote, and of the way that he drove the rest of us with him, and I knew that he was right.
There is a fury to Terry Pratchett's writing: it's the fury that was the engine that powered Discworld. It's also the anger at the headmaster who would decide that six-year-old Terry Pratchett would never be smart enough for the 11-plus; anger at pompous critics, and at those who think serious is the opposite of funny; anger at his early American publishers who could not bring his books out successfully.
And that anger, it seems to me, is about Terry's underlying sense of what is fair and what is not. It is that sense of fairness that underlies Terry's work and his writing, and it's what drove him from school to journalism to the press office of the SouthWestern Electricity Board to the position of being one of the best-loved and bestselling writers in the world.
This description of Terry Pratchett reminded me of the character Sam Vimesfrom the Discworld series. Vimes is an idealist, but a committed cynic whose knowledge of human nature constantly reminds him how far off those ideals are. Vimes also has a dark side that comes out when Vimes loses control of his anger, especially when he temporarily lets go of "the Beast" (in the novel Thud!).