Halo announcement trailer
From Halopedia, the Halo wiki
The Halo announcement trailer first unveiled Halo: Combat Evolved to the public at Macworld 1999 running in real-time on a Power Mac G3 with Rage 128. At this point in development, Halo was still a third-person shooter for the Mac, and while this early build of the game differed heavily from the retail version, it featured recognizable core elements such as Spartan-II supersoldiers, Elites, and the Warthog.
The trailer begins with a Spartan-II in an early version of Alpha Halo's Control Room, seemingly doing some operations with The Core. He then runs away, and ends up in a hangar with a few Banshees and two Elites with Energy Swords. He taunts the Elites, and runs through some Forerunner corridors as they chase him. He exits into an open hilly area, with a Warthog and two other Spartans, one of whom is firing an assault rifle. Gesturing with his hands, all three Spartans then jump into the Warthog and drive across the hills, the Elites unable to catch the vehicle.
As the Warthog drives through the hills, two Elites spot it and give chase with their Ghosts. The Warthog opens fire with its M41 LAAG and manages to flip one Ghost over, after which the other gives up. The Warthog then stops and the Spartans disembark, spotting a Banshee guarded by two Elites down in a valley. One of the Spartans jumps into the Warthog and drives past the Elites, distracting them. The second Spartan jumps behind the Plasma Rifle-wielding Elite and points a Pistol at his head, making the Elite surrender. The third one makes a run for the Banshee and takes off, avoiding blasts from the second Elite's Fuel Rod Gun. The Banshee flies across the landscape, and another Spartan is seen atop a tall hill, waving a Bungie flag.