The personal papers of Alan Rickman reveal the late actor was "frustrated" by one of his most famous roles – Severus Snape, the sneering teacher of the Harry Potter films.

An archive of papers belonging to Rickman, who died in 2016, was presented for sale at this week's ABA Rare Book Fair in London – including a postcard from David Hayman, the producer who cast Rickman in the role of Snape.

"Thank you for making [2002's Harry Potter and the Chamber of Secrets] a success", Hayman writes. "I know, at times, you are frustrated but please know that you are an integral part of the films. And you are brilliant."

A note written by the actor while working on 2009's Harry Potter and the Half-Blood Prince suggests he was unhappy about the lack of attention given to his character. Until the heading "Inside Snape's Head", Rickman wrote: "It’s as if [the film's director] David Yates has decided that this is not important in the scheme of things i.e. teen audience appeal."

The full archive, which has been valued at £950,000, includes letters from the Prince of Wales, Bill Clinton and Tony Blair, as well as Harry Potter author JK Rowling, who thanks Rickman for "doing justice to my most complex character."