Bernie Sanders and Larry David are distant (maybe third?) cousins, which they didn’t know until they appeared on Finding Your Roots.
Actor/writer David Hornsby (It’s Always Sunny in Philadelphia, Mythic Quest) and musician Bruce Hornsby are cousins.
This one is fairly well-known, but Mike Nesmith (Monkees guitarist and music video pioneer) is the son of Bette Nesmith Graham, a secretary who invented Liquid Paper and built it into a successful company.
Singer Carly Simon’s dad is the Simon from publisher Simon & Schuster.
Similarly, Ralph Lauren’s daughter Dylan has a chain of candy stores. Honestly, in both cases, having a wealthy father must have helped.
Markie Post, from Night Court, was the daughter of Richard Post, a fairly well-known physicist. He taught a graduate class in electromagnetism I took. Great guy.
The actor Justin Theroux is the nephew of the novelist Paul Theroux, who is the father of the documentary filmmaker Louis Theroux, with various other prominent people in the family.
(Honestly, imagine being in a high-achieving family like this and having no ambition or ability or just being a fuck-up.)
Elon Musk’s mother, Maye, is a successful fashion model.
Brad Pitt’s brother, Doug, is apparently a renowned philanthropist.
FedEx founder Fred Smith’s son Arthur is the head coach of the Atlanta Falcons.
Screenwriter, author (of World War Z) and voice actor Max Brooks is the son of Mel Brooks.
Author Kurt Vonnegut’s brother Bernard was a renown weather scientist who discovered that silver iodide could be used to seed clouds and produce rain if conditions were right
Brother of Isaac Asimov, Stanley Asimov was a noted journalist who worked for and helped produce Newsday.
Author David Sedaris, his sister: actress Amy Sedaris
Continuing in a “north of the 49th” theme, Kiefer Sutherland’s maternal grandfather was Tommy Douglas, former premier of Saskatchewan, and the main political figure behind Canada’s universal health care system
Woody Harrelson: actor. His father Charles was a mob hitman.
Beat generation SF author William S. Burroughs is the grandson of the Burroughs Adding Machine company founder, William Seward Burroughs.
Author Larry Niven is the descendant of the oil magnate Edward Laurence Doheny - the person whose life “There Will Be Blood” is loosely based on. Doheny was also a key player in the Teapot Dome scandal - he was acquitted of bribing an official (who was convicted of taking a bribe - who said the law is logical).
Also, Stanley Asimov’s daughter Nanette Asimov (and Isaac’s niece) is a longtime reporter for the San Francisco Chronicle.
The Wikipedia page for Justin Theroux, mentioned by @Dewey_Finn above, shows links to 7 relatives of his who are prominent enough to have their own Wikipedia pages. The page for Cary Elwes shows 15: Cary Elwes - Wikipedia
Most of them were famous in their own time but not today; maybe the most recognizable name is his stepfather Elliot Kastner. Still, it makes me wonder how many other people who aren’t royalty or Kennedys would have that many Wikipedia connections. Cary Elwes’s connections include 2 of his siblings, his father and paternal grandfather (who were both painters) and great grandfather (a diplomat) several great uncles (all clerics) his mother, stepfather, and maternal great-grandfathers.
Bruce Springsteens daughter won a silver medal in 2021 Olympics in Equestrian
Bret Hedican won a Stanley Cup and his wife Kristi Yamaguchi won a gold medal in figure skating. And she also won dancing with the stars
And his son Eric is the chief wine critic for the New York Times.
Wallace Shawn is the son of longtime New Yorker editor William Shawn.