It's obvious from Judge Pyncheon's first appearance in the novel that he is his ancestor Colonel Pyncheon reborn. Hepzibah sees it, Clifford sees it, even Mr. Holgrave's camera sees it. Sure, there are plenty of differences between the two men: physically, Judge Pyncheon is smaller and paler than his forebear. Colonel Pyncheon worked his way through three wives, while Judge Pyncheon only had one (who could only stand four years of being married to him before she died). Colonel Pyncheon had children and grandchildren, while Judge Pyncheon has just one son, who dies while abroad. One last difference: Colonel Pyncheon's face is stern and strong. Judge Pyncheon has found a way to hide his sternness and strong will behind an "exceedingly pleasant countenance" (6.19). Everyone thinks he has "a very pleasant smile" (4.20).
Despite these cosmetic differences, at heart they are the same guy. Both are prominent public men; in fact, Judge Pyncheon is about to nominated as a candidate for governor of Massachusetts by his political party. Both are financially very successful. Both have a will of iron. Both give to the right social causes and support respectable church activities. And both are bottomlessly greedy. Hepzibah accuses Judge Pyncheon of bringing back to life "this hard and grasping spirit" that "has run in [Pyncheon] blood these two hundred years" (15.41). Judge Pyncheon is proof that you can inherit evil: Colonel Pyncheon frames a man for witchcraft and, lo and behold, his however-many-great-grandson Judge Pyncheon also frames a man for murder – and all for money.
Judge Pyncheon's specific rise to self-righteous power happens as follows. First, he's a bad kid. In the words of the narrator, his "brutish [...] animal instincts" develop earlier than his "intellectual qualities" (21.5). He is addicted to "low pleasures" (21.5) and, as a result of his drunkenness and wildness, he falls out with his elderly uncle, Jaffrey Pyncheon. One night Jaffrey the Younger breaks into his uncle's study and starts searching for money. Uncle Jaffrey Pyncheon walks in on his nephew and suddenly dies of a stroke. Jaffrey the Younger has the great idea of using Uncle Jaffrey Pyncheon's death to make it look like his cousin Clifford (a nice boy who lives in the House of the Seven Gables with his uncle) murdered the old man. Thanks to Jaffrey the Younger's testimony, Clifford gets locked away in prison for 30 years. Jaffrey the Younger gets his uncle's money and his cousin Hepzibah gets the House of the Seven Gables.
Now, 30 years later, Judge Pyncheon is a rich man. After his uncle's death, he used his inheritance to sober up and build a respectable life for himself. He has become politically important in Massachusetts and all seems to be going well. But he's still nagged by something: he believes that some part of his inheritance from Uncle Jaffrey Pyncheon has gone missing. And he thinks that poor Clifford holds the secret to this lost wealth. So he arranges for Clifford to be released from prison and demands to see the poor man. Hepzibah protests that seeing Judge Pyncheon will drive Clifford crazy. She also has no idea why Judge Pyncheon can't let this go. He already has plenty of money, more than enough to leave to his son. By threatening Clifford, all Judge Pyncheon is doing is carrying on the Pyncheon family curse.
Judge Pyncheon thinks this is all nonsense. He forces his way past Hepzibah into the House of the Seven Gables. There he sits down in the parlor on the chair where Colonel Pyncheon is supposed to have died, and suddenly he has a stroke. His abrupt death leaves Hepzibah and Clifford free to leave the House of the Seven Gables at last. With Judge Pyncheon's death and Phoebe's marriage to Mr. Holgrave (a descendant of Matthew Maule), the Pyncheon family curse seems to be lifted.
One last note on Judge Pyncheon: after his death, there is an absolutely fascinating and bizarre chapter called "Governor Pyncheon" (Chapter 18). The form of this chapter is a direct address to Judge Pyncheon's dead body. The narrator reminds the Judge to get up, get up – he has a busy evening planned. He is about to be nominated governor. He also has to visit his stockbroker and buy a new horse. And he is supposed to see the doctor about this odd dizziness he's been feeling lately – surely nothing important. But of course, Judge Pyncheon never rises.
Why does Hawthorne spend a whole chapter addressing Judge Pyncheon's corpse? We can't say for sure; all we can do is throw out an idea. We think Hawthorne is trying to underline the message that death comes to all of us in the end, no matter how busy or important we are. Judge Pyncheon spends his whole life trying to add more to his estate – but to what purpose? As the expression goes, you can't take it with you! All of these important appointments with the movers and shakers of the Massachusetts political world don't matter at all when he's dead. What's more, once Judge Pyncheon has died, he has lost his opportunity to atone for his sinful behavior towards his cousin Clifford. As the narrator points out, "the Avenger is upon [him]!" (18.26). He has lived his life, and now it's Judgment Day.
The final paragraph of this chapter, as we follow a housefly landing on Judge Pyncheon's still face, demonstrates that he is truly dead. There is nothing left of him but a corpse, no matter how respectable and frightening he might have seemed in life. Death has deprived Judge Pyncheon of all his power and intimidation – he's just an empty body by the end of Chapter 18. With this transformation into a corpse, Judge Pyncheon can become evidence to prove Clifford innocent of murder: once everyone sees the symptoms of Judge Pyncheon's natural death, they realize that Uncle Jaffrey Pyncheon died a similar natural death 30 years before. So not only has Judge Pyncheon become nothing more than a body by the end of the novel, but he has also become the thing that clears Clifford Pyncheon's name! There's poetic justice in that.