Which Discworld should you read first? Here have this friendly flowchart, start at the Upper left corner, the orange bubble.

The current Patrician, head of the extremely rich and powerful Vetinari family, was thin, tall and apparently as cold-blooded as a dead penguin. Just by looking at him you could tell he was the sort of man you’d expect to keep a white cat, and caress it idly while sentencing people to death in a piranha tank; and you’d hazard for good measure that he probably collected rare thin porcelain, turning it over and over in his blue-white fingers while distant screams echoed from the depths of the dungeons. You wouldn’t put it past him to use the word ‘exquisite’ and have thin lips. He looked the kind of person who, when they blink, you mark it off on the calendar.
Practically none of this was in fact the case, although he did have a small and exceedingly elderly wire-haired terrier called Wuffles that smelled badly and wheezed at people. It was said to be the only thing in the entire world he truly cared about. He did of course sometimes have people horribly tortured to death, but this was considered to be perfectly acceptable behaviour for a civic ruler and generally approved of by the overwhelming majority of citizens.

Pratchett, Terry. Sourcery: (Discworld Novel 5) (Discworld series) (pp. 73-74). Transworld. Kindle Edition. 

Introducing *drum roll* Havelock Vetinari

This is the first canon description of the Havelock we know and love from all the following books. I refuse to believe the fat, jellyfish guy in The Colour of Magic is the same person - no matter what TP vouchsafed on the subject. 

I base a lot of his character in my fanfiction on the notion that Havelock Vetinari appears to be one thing- scary, sadistic, tyrannical, pretentious - but is in reality a brilliant man who decided to help Ankh-Morpork prosper because he can. 

This is basically canon because TP elaborated in Making Money.

…I’m betting on a man who thinks war is a wicked waste of customers. A man who’s a better con artist than I’ll ever be, who thinks committees are a kind of wastepaper basket, who can turn sizzle into sausage every day …

Pratchett, Terry. Making Money: (Discworld Novel 36) (Discworld series) (p. 453). Transworld. Kindle Edition. 

Havelock is a con-artist in the sense that he lets everyone believe he is a tyrant as per definition above but is really only interested in keeping the city going for the city’s sake, not his own.

Vetinari’s core motivation is revealed in the underrated gem, Unseen Academicals.

And that’s when I first learned about evil. It is built in to the very nature of the universe. Every world spins in pain. If there is any kind of supreme being, I told myself, it is up to all of us to become his moral superior.’

Pratchett, Terry. Unseen Academicals: (Discworld Novel 37) (Discworld series) (p. 295). Transworld. Kindle Edition. 

Despite his own assertion to Vimes in Guards!Guards! that he is evil, and indeed he does believe evil is at the centre of everything, he strives to be better than just that. 

In that sense he and Vimes are very much alike. The only difference is Vimes struggles with the concept that evil is build in, whereas Havelock has embraced it. Alas, both men are striving to be better.

“High over the Circle Sea Rincewind was feeling a bit of an idiot.

This happens to everyone sooner or later.

For example, in a tavern someone jogs your elbow and you turn around quickly and give a mouthful of abuse to, you become slowly aware, the belt buckle of a man who, it turns out, was probably hewn rather than born.

Or a little car runs into the back of yours and you rush out to show a bunch of fives to the driver who, it becomes apparent as he goes on unfolding more body like some horrible conjuring trick, must have been sitting on the back seat.

Or you might be leading your mutinous colleagues to the captain’s cabin and you hammer on the door and he sticks his great head out with a cutlass in either hand and you say ‘We’re taking over the ship, you scum, and the lads are right with me!’ and he says ‘What lads?’ and you suddenly feel a great emptiness behind you and you say ‘Um …’

In other words, it’s the familiar hot sinking feeling experienced by everyone who has let the waves of their own anger throw them far up on the beach of retribution, leaving them, in the poetic language of the everyday, up shit creek.”

Terry Pratchett, Sourcery

It’s the familiar hot sinking feeling experienced by everyone who has let the waves of their own anger throw them far up on the beach of retribution, leaving them, in the poetic language of the everyday, up shit creek.
—  Terry Pratchett - Sourcery