Here's a few regarding Fresh Prince of Bel Air
The show originally had nothing to do with Will Smith, it was pitched as a show about the life of Talent Manager Benny Medina, who actually was living in the ghetto before living with his rich relatives.
He pitched it to Quincy Jones, who liked the idea but turned it down because it was too similar to every other white sitcom, and they both agreed the lead should be black to make it stand out.
It was pitched to NBC who loved the idea, and it just so happened around that time, Will Smith was having issues regarding his taxes, and by pure chance, Smith and Madina met.
Will took the offer, show was picked up, and it ran for 3 seasons.
And before you say "wait there's 6 seasons of Fresh Prince!"
It originally ran for 3 seasons, but fan demand and persuasion from Warner Bros TV (who owns the distribution rights) to give the show more episodes for a better syndication package, convinced NBC to give the show a few more seasons, where it actually ended since Will Smith thought the show needed to end.
Here's another one