Simon came up with the idea of Jane having a couch as it served two purposes. 1) It reminded him of a therapist who can read and analyse people, just like Jane and 2) He could get to sit down at all times! The couch was meant to be 'slick yet messy', just like Jane.
Jane's suits were meant to always look wrinkled and crumpled as Jane stored them all in a drawer and not hung-up in a wardrobe. He also never ironed his suits.
CBS originally wanted Jane to drive a Taurus but Simon wanted a different car. He visited a movie lot with many cars used in films and chose the 1970s Citroen DS Pallas. The original colour of the Citroen was red but they resprayed it blue to match Jane's aesthetic.
Jane was written to wear sandals all the time but Simon suggested the fan favourite old brown shoes.
Jane is a working class Irish last name.
Teresa Lisbon
Lisbon was originally meant to be half Irish and half Portuguese.
Lisbon was meant to have 4 brothers.
The Lisbon brothers were originally meant to all be policemen or fireman (like Teresa and her dad respectively) with Tommy being the black sheep.
Jane and Lisbon were meant to have more of an enemies-to-friends dynamic but this changed thanks to the friendship between Simon and Robin.
Kimball Cho
Cho's millitary background became a pivotal part of his character after discussions with Tim and the producers.
Cho was meant to be a family man but Tim was given the freedom, to change Cho's background and character. In fact, all the actors were allowed to flesh out their characters by coming up with their backstories.
Wayne Rigsby
Rigsby was meant to be the 'frat jock guy' and 'popular with the ladies' but his character was changed thanks to Owain's personality and skill set.
The characters of Jane and Rigsby are the ones to be shown eating more than a bite of food. Owain remarked years later in a 2019 interview for Emergence that he put on weight from all the eating as tv food = real pounds so he had to start working out more.
The CBI Building
The CBI headquarters were made to look like an old Sacramento shipping company which is why there are faded adverts and slogans outside Jane's attic. The CBI building facade is actually the Pico House in downtown LA.
Red John
Red John's smiley face calling card is based on a real serial killer nicknamed the Smiley-Faced Killer who left smiley faces by the bodies.
Originally, Red John's arm was meant to be shown in scenes and there is a deleted scene in 1x01 where RJ has a tv screen and a cup of tea watching Jane.
Facts credited to TheMentalistHQ on Twitter and various interviews.
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