The number first appeared in the game System Shock (as 451) and its sequel System Shock 2 (as 45100) developed by Looking Glass Studios. It is a reference to Ray Bradbury's dystopian novel Fahrenheit 451, in which it represents "the temperature at which book-paper catches fire and burns". 0451 was also the door code to access the Looking Glass Studios offices. The code 0451 has since appeared in numerous other games developed by former Looking Glass employees, including Deus Ex, Bioshock, Dishonored and others.