The battle between Gandalf the Grey and the demonic Balrog is one of the highlights of The Lord of the Rings trilogy, first conceived by author J.R.R. Tolkien and later brought to memorable life in a pair of movie adaptations. Director Peter Jackson's take on the scene has become a signature of his celebrated trilogy, with actor Ian McKellen's thundering "YOU SHALL NOT PASS!!!" practically a catchphrase. The scene works because of its inherent drama and spectacle, but it's also deeply tied to Tolkien's extremely thorough world-building. The Balrog's presence in the Mines of Moria is no accident, with a lengthy backstory stretching to the earliest days of Middle-earth.
Source：https://www.cbr.com/lord-of-the-rings-gandalf-balrog-speech/
