Kitty Pryde was technically in the original X-Films, but it wasn't until The Last Stand with Ellen Page in the role that she was given anything to really do. She was there to be one of the sides in a love triangle between Rogue and Bobby Drake with very little else to it. It was underwhelming.
Without going into the entire history of Kitty Pryde and her myriad of codenames, her introduction to the X-Men comics was a huge event in the war between the Hellfire Club and the X-Men.
X-Men #131 as a whole is Kitty Pryde being recruited while both groups vie for her to join their side. More than being the last leg before the Dark Phoenix Saga, it was a story filled with the basics of who the X-Men are and why they are not just another superhero group. It was also a pivotal moment bringing in a young Jewish girl to act as an audience proxy and fully incorporate what being a 'gifted youngster' would be.
She's become a staple character in the comics, and something like this introduction is needed in future films.
Learning to read from his parents' old comic book collection, ink has flowed through his blood since he was born! And now, the self-proclaimed Comic Archivist (at least on Youtube) brings his talents for comic book history and obscurity to WhatCulture! Be warned: he's a Cyclops fanboy and a Nightwing groupie!