From the ever-inventive brain of HG Wells comes The War Of The Worlds’ three-legged walkers, an army that have been represented in many different ways on both the page and the screen. They may appear different from time to time but the Tripods are always used for the same reason, to help Martians invade Earth. With flailing metallic tentacles used to gather up hapless humans below, the Tripods also have a very destructive heat ray and a poison gas cloud at their disposal. In Steven Spielberg’s 2005 imagining the Tripods were buried underground long ago as part of an alien contingency plan and are unearthed when the aliens travel to Earth. With ample firepower and decent defence systems (an invisible force field), the Tripods are a formidable foe. Its design has influenced a great many other sci-fi armies, including the Striders in videogame Half Life 2 and the Star Wars AT-ST walkers – though you didn’t hear that from us, we don’t need Lucas’s lawyers on our backs.