How would Microsoft have fared in a Bungie-free world? A world where its masterful space opera hadn’t greased the Xbox slip road with high-grade Warthog engine oil? The system’s first and biggest star has flared brighter still since its appearance, two console generations ago, but on launch day it was just as renowned for not being Sneakers or Mad Dash Racing as it was for forging the future of the FPS.

Bungie co-founder Jason Jones most likely had no conception of what lay ahead when he clambered onto the stage at Macworld 1999 to put a name and a look to the company’s next endeavour. This was Halo’s public debut, eliciting zero groans of space marine fatigue as the sub-genre was still relatively virgin territory. Besides, a brand with Bungie’s hard-built name recognition behind it was never one to underestimate.

The game already had two years of work in the bag and some fundamental changes both behind and ahead of it, riding out an evolutionary arc from RTS origins through third-person action to FPS. Of course the biggest upset would be the Microsoft buyout in 2000, leading to the wholesale move of Bungie from Chicago to Redmond, and Combat Evolved's sideways strafe from PC and Mac exclusive, to Xbox launch title…

At this point Xbox Live was still in development, so online multiplayer was never going to happen for Halo. Instead, system-link play took the baton and sprinted with it, while split-screen co-op in the solo campaign offered social play for those who didn't want to heft the rather weighty original Xbox to a friend's home.

And the scale of that solo campaign was impressive at the time. It follows the last SPARTAN-II super-soldier taking flak on the titular ringworld and a succession of ships and stop-offs, each one a firefighting hotspot bubbling over with Hunters, Grunts, Jackals, Elite and the Flood. A smart balance of offence and defence in the streamlined two-weapon system and regenerating shields makes for fast, uncluttered gameplay spearheaded by an iconic man-tank of an action hero. The well-judged difficulty settings also scale the challenge beautifully for co-op.

Microsoft stated from the start that Bungie would play ‘a key role’ in the future of Xbox – which turned out to be a rather impressive understatement. And behind Halo’s stellar budget and scope Combat Evolved is recognisably Bungie, from the quirky chapter titles to the UNSC battlefield banter and under-fire panic attacks of the nervous Covenant Grunts.

Sometimes the modern influence of our legends of gaming, regardless of their impact crater back in the day, is tough to quantify. But despite Halo now being almost old enough to legally play itself, you’d have to be living under a rock in a witness protection scheme with the full compliance of all neighbouring rocks to have missed the series’ stratospheric trajectory.

Marathon’s cult following was minuscule compared to this. Imitated but never bettered, each new sun-sized Halo hit shattered the standing sales record of the last. Now it’s up there with the likes of GTA, Mario and Assassin’s Creed. But you can’t fish in the same stream forever, and after five games Bungie stepped away from a brand that regularly hit the high 90s in reviews and topped 50 million copies – using the money from this rampant success to buy back its independence.

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