Sir Christopher Lee (Saruman) read "The Lord of the Rings" once a year until his death in 2015, and had done so since the year it was published. He was also the only member of the cast and crew ever to have met J.R.R. Tolkien.
Director Sir Peter Jackson gave one of the rings used in the movies to Elijah Wood and Andy Serkis as a gift when the shoot was finished. They both thought they had the only one. But both of them were deceived.
Gandalf's painful encounter with a ceiling beam in Bilbo's hobbit-hole was not in the script. Sir Ian McKellen banged his forehead against the beam accidentally. Sir Peter Jackson thought McKellen did a great job "acting through" the mistake, and kept it in.
During filming, most of the members of the Fellowship took up surfing in New Zealand in their spare time. Amongst them was Viggo Mortensen, who wiped out terribly one day and bruised one whole side of his face. The next day, make-up artists tried to mask the bruising and swelling, but were unsuccessful. Instead, Sir Peter Jackson opted to film Mortensen from one side for the entire scene. In the Mines of Moria, when they find the tomb, Aragorn is only seen from one side in the whole scene.
The cast often had to fly to remote shoot locations by helicopter. Sean Bean (Boromir) was afraid of flying and would only do it when absolutely necessary. When they were shooting the scenes of the Fellowship crossing the snowy mountains he'd spend two hours every morning climbing from the base of the mountain to the set near the top, already dressed as Boromir. The crew, as they were flown up, could see him from their helicopters.
Alan Lee: In the prologue, one most famous Middle-earth artist can be seen as one of the nine human Kings.
Zo Hartley: A Hobbit couple, who were about to kiss, before the other ate a cupcake instead, in the Extended Edition.
Michael Elsworth: Cirdan the Shipwright in the left of Gil-galad and Galadriel during the prologue, and an archivist who escorts Gandalf to the archives in Minas Tirith.
Gino Acevedo, Xander Forterie, Richard Maybery: Weta Workshop artists as Dwarf-lords during the prologue.
Peter Jackson: [children] Jackson's children Billy Jackson and Katherine Jackson are listed in the end credits as "Cute Hobbit Children."