In "Irrational Treasure," they celebrate Pioneer Day with Pacifica, their daughter. They pose together for a family photo after the opening ceremony, and later they both laugh at an insult Pacifica makes to Mabel before going home.
In "The Golf War" they are seen at Ye Royal Discount Putt Hutt with Pacifica, and they stand by as she insults the Pines family. They later bring Pacifica back to the mini golf course for her competition against Mabel, reminding (and pressuring) her to win. They do not stay to watch because they have a party to attend.
In the "Society of the Blind Eye" it was revealed that he has had his memories erased. His memories may have been heavily linked to the goings-on of the Blind Eye Society, since it was on the shelf in The Hall of the Forgotten, next to McGucket's memories. It is possible that Preston's tube is also on a pressure-sensitive plate.
In "Northwest Mansion Mystery," he and Priscilla are preparing for their massive annual party, open only to the rich and the super-rich. He is shown to ring a bell to silence Pacifica into obedience whenever she speaks out. He was also aware of the curse placed upon the family by the Ghost of Northwest Manor, but refused to allow the common folk in, fearing that his family's reputation would be ruined. Instead, he has Pacifica recruit Dipper to deal with the ghost, making her keep the real reason for the haunting a secret. After Dipper captures the ghost, he is told of the reasons for his cursing the Northwest family, and Dipper angrily confronts the Northwest family. Preston coldly rejects Dipper's tirade, and prevents Pacifica from telling Dipper that he forced her to lie. When the ghost escapes and starts turning the guests to wood, Preston has his family and butler hide in a panic room, leaving their guests to their fate rather than break the curse by letting in the common folk. However, Pacifica stands up to her father, opening the gates and breaking the curse, leaving Preston dismayed at all the "riff-raff" entering the party.
Mr. Northwest enjoys being wealthy and takes pride in being a descendant of Nathaniel Northwest, the alleged founder of Gravity Falls, Oregon. It appears that he and Priscilla Northwest are as snobbish as their daughter, and support her being rude to others. However, Preston proves to be significantly worse than he initially seems.
He is revealed to truly be a ruthless, callous man who sees anyone of lower class as simply tools to be manipulated. He also doesn't seem to care for his fellow rich that much either, being willing to leave others to their deaths if it means preserving the Northwest family name, as shown when he tries to persuade Pacifica from opening the gates to their party rather than breaking the curse. He is extremely controlling and emotionally abusive to Pacifica, using a bell to keep his daughter in check to his standards. It's implied he doesn't truly care for Pacifica either, and simply sees her as a tool to maintain the Northwest name. 
Preston Northwest has short dark brown hair and a dark brown mustache. He has prominent cheekbones, and a large, rectangular nose. For Pioneer Day, he dressed up in a top hat and a suit similar to Priscilla's dress. He wears a gold ring on his middle finger on his left hand. He generally wears a black suit with a white undershirt, and a green tie.
- 203. "The Golf War"
- 207. "Society of the Blind Eye" (mentioned)
- 210. "Northwest Mansion Mystery"
- 215. "The Last Mabelcorn" (pictured)
- 217. "Dipper and Mabel vs. the Future" (no lines)
"Good one, daughter!"
"Oh, and whatever happens, just remember one thing: you're a Northwest. Don't lose."
"Look at who you're talking to, boy. I'm hosting a party for the most powerful people in the world. Do you think they'd come here if they had to rub elbows with your kind?"
"Pacifica Elise Northwest, stop this instant! We can't let the town see us like this! We have a reputation to uphold! Now come into the panic room, there's enough mini-sandwiches and oxygen to last you, me, and a butler for a full week. (whispering) We'll eat the butler!"
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