This is for scripted shows only, no reality.
Agnes Moorehead was a devout Christian irl who played Endora on Bewitched. Endora was based on the very wicked witch of Endor from the Bible.
Besides Marilyn, all the Munsters actors looked nothing like that irl.
As far as we know, Brent Spiner (Data) is not an android. ;)
David Duchovny and Gilliian Anderson's real life positions on aliens were the reverse of their X-Files characters.
Iain Armitage seems like a normal boy irl, not at all a pretentious snob like his Young Sheldon character.
Samantha had great chemistry with Dick York's Darrin. Sadly Elizabeth Montgomery was nasty towards him in real life and hated Dick York for no good reason. Considering her real husband was the producer of Bewitched, he wouldn't have said good things about Dick York if her lies about him were true.
Bill Cosby the serial rapist of course was the polar opposite of his Cliff Huxtable character. He sure had a lot of people fooled though thinking he was a good person until this past decade.
Grace Kelly was a funny likable lead. Brett Butler though, was such a troublemaker behind the scenes, probably why season 5 was abruptly cut short as Grace Under Fire still got good ratings.
The 828ers on Manifest weren't really raised from the dead.
Womanizing Bulldog (Dan Butler) on Frasier was gay irl.
Ted Levine irl is probably nothing like the monster he plays on Big Sky, don't know how close he is to his Monk character.
Jack Benny's cheapskate and terrible violinist act was not true irl.
Whoopi Goldberg is an obnoxious and rude person irl. But she played likable characters such as Guinan (Star Trek: TNG) and Delores in the Sister Act movies. Her Blue Bloods character, though, is probably close to her real self.
Frances Bavier was really mean irl, nothing like her genial Aunt Bee character.

Steve Landesburg was not the genius he portrayed as detective Arthur Dietrich on Barney Miller.

Hal Smith was not the alcoholic he portrayed as Otis Campbell on The Andy Griffith Show. Andy Griffith said he did not drink in real life.

Jim Backus was not as generous as the wealthy millionaire Thurston Howell III on Gilligan’s Island. Dawn Wells said he would often invite her and other cast members to lunch, but he’d conveniently always forget his wallet.

Fred Grandy was not a bumbling ship attendant as on The Love Boat but a super smart magna cum laude graduate of Harvard who served 4 terms in the United States Congress.

Carroll O'Connor was not like "All in the Family's" Archie Bunker as he was a hardcore liberal IRL.

Carroll O'Connor was not like "All in the Family's" Archie Bunker as he was a hardcore liberal IRL.

Almost every actor is a hard core liberal in real life.

Fred Grandy, who served in Congress as a Republican, is an exception.

Here are two from Happy Days. Henry Winkler is almost the total opposite of The Fonz. Anson Williams, in reality he is a very smart man. Quite different from Potsie, especially the Potsie character from the later seasons.

Another one is Suzanne Somers, also a very intelligent lady and quite different from the Chrissy character on Three's Company. Generally at least when it comes to classic TV shows, I find many of the actors and actresses that played characters that are not that smart are in reality are very intelligent.

Betty White played the rather dumb, goofy, and head scratchingly idiotic Rose Nylund on The Golden Girls from 1985-1992. Despite that, Betty White, to my knowledge, is a very wise, sensible, content, witty, smart person.

I wanted to do a thread of actors in roles who basically played themselves.

On the Andy Griffith Show for example, everyone says that Howard McNear who played Floyd the Barber was about the same person. Basically he played himself as a barber in a small town.