From an interview with M. Night Shyamalan:
I wrote this character [Kevin] and a bunch of the scenes you saw in
the movie for the Unbreakable script. He was the original antagonist
and David Dunn was going to meet him in the original script.
couldn’t get it right, I couldn’t get the balance right. It just kept
wanting to eat away at the other movie. I pulled Kevin out. I wanted a
really slow burn movie and Kevin’s not a slow burn. I said, ‘let me
pull him out for a second and concentrate on these other two
I came up with the idea for Elijah [Mr. Glass, the
character played by Samuel L. Jackson in Unbreakable]. He was always
an advisor. The three of them were always in it but he went from
benevolent advisor to the opposite of David Dunn! It became so
Then I said I’d do this next as the next piece in this, but I
guess I felt that the reaction at the time was weird and wonky to
Unbreakable, especially in the United States. ‘What is this? A movie
about comic books?’ The studio didn’t want to sell it as comic books
because they felt comic books were not sellable, they didn’t think
there was an audience for it.
He is already working on continuing the story:
I’m writing the outline now. It’s weird. It’s long. It’s the longest
outline I’ve ever had. It’s almost ten pages of an outline. I don’t
know what that means. It’s very long. It has so many characters. It’s
a weird process.
I already know all the characters, or most of them. I
know 80% of the characters, so the discovery process isn’t there. It’s
easy to write, which I’m very suspicious about. There’s not been a lot
of bloodshed yet.
I hope if Split is a success, I’ll have the
opportunity to finish the story. I want to finish it, so this is the