We don't see much of old Colonel Pyncheon. He only appears physically in the first chapter (unless you count his portrait and ghostly manifestations, which we talk about in "Symbolism, Imagery, Allegory"). But for a dead guy, he has an enormous effect on the plot of the novel.
Colonel Pyncheon is the founder of the Pyncheon family in Massachusetts. He is a rich, well-respected man, equally admired by Puritan clergymen and government types alike. No one will say a bad word about him – in public. But in private, village gossip shows another side of Colonel Pyncheon: he's a stern, self-righteous guy. He's good at getting ahead in the world, but he has no mercy or sense of shame. And only someone who combines lots of energy with no scruples would be able to achieve what Colonel Pyncheon manages.
Colonel Pyncheon has a big plot of land. But he wants to build his house on the one acre next to his land that happens to belong to somebody else, Matthew Maule. Maule is a carpenter and has no public influence or power. All the same, he stands up to Colonel Pyncheon and refuses to sell his property. Colonel Pyncheon isn't one to give up, though: when the witchcraft scare of 1692 sweeps through Salem, Colonel Pyncheon leads the accusers against Matthew Maule. Maule is tried, condemned, and hanged. And without batting an eyelid or thinking twice, Colonel Pyncheon immediately starts to build his house on the foundations of the dead Maule's old hut. What's more, he hires Matthew Maule's own son, Thomas Maule, to lead the project! This is not a guy with a lot of tact.
Of course, the legend goes that Matthew Maule put a curse on Colonel Pyncheon, that "God will give him blood to drink!" (1.4). When Colonel Pyncheon is found dead on the day of his housewarming party while sitting under his own portrait, the story of Maule's prophecy really starts to take hold. The whole village agrees that the Pyncheon family – no matter how well-respected and wealthy they may be – is cursed.
Colonel Pyncheon embodies a lot of virtues that were important to the early English settlers of Massachusetts: he is energetic, he has a strong will, and he is good at accomplishing things. The flip side of this strength of character is that he is self-righteous and willing to squash other people to get his way. The official record of the early Puritan settlements of Massachusetts is full of guys who were well-respected leaders of men (including Hawthorne's own ancestors, William Hathorne and John Hathorne). But look what these traits lead to: witchcraft trials and persecution of people with non-Puritan religious beliefs. Even though these early Puritans gave off the appearance of holiness, they could be a tough, unjust bunch. And Colonel Pyncheon presents precisely this conflict between public respectability and private cruelty.
Once Colonel Pyncheon dies, the bad blood between the Pyncheon and the Maule families isn't resolved. The thing is, Colonel Pyncheon may have died, but the idea of him persists. Not only does he order that his portrait be left on the wall of his family home to remind his descendants of where they come from, but he has also leaves traces of his hard, tyrannical manner on each generation of Pyncheons to come. And that is the true curse of the Pyncheon family: it isn't Matthew Maule's "blood to drink," it's the greedy cruelty inherited from Colonel Pyncheon that keeps bringing so much sorrow to the Pyncheon line. (For more on Hawthorne's real-life inspirations for the character of Colonel Pyncheon, check out "In a Nutshell.")