Can you imagine Portal without GladOS?

Well, according to an interview with PC Gamer with Valve's Robin Walker, after almost a full year of development work, GladOS didn't even exist yet. At that point, the game was partially playable, with 14 fully functional levels. But the deceptively evil AI, voiced by Ellen McLain, that forms the beating heart and soul of Portal was nowhere to be found.

The interview and GladOS revelation comes on the 10th anniversary of The Orange Box. Valve's 5-in-1 games collection is also notable for bringing Half-Life 2 and Team Fortress 2 to consoles, but its biggest hindsight success is unquestionably Portal.

Valve realized during the game's early playtests that it wasn't clicking with players. The notion of a first-person puzzle game was a foreign concept at that point, and that meant anyone who sat down to play didn't have a frame of reference to guide them.

"Players were having fun, but they seemed to consider everything they played as just training leading up to something else"

"There was no GladOS, the player just moved from puzzle to puzzle without any sense of progression or reward beyond the increasing complexity of the puzzles," Walker explained. People were enjoying the core mechanics, but they felt it was all just an extended tutorial.

Summed up, the prevailing attitude was: "This is really fun! When does the game start?"

"Players were having fun, but they seemed to consider everything they played as just training leading up to something else," Walker said. "Considering the entire game was really just a process of learning about the core gameplay mechanic, this scared us a lot, making us worry that we’d have to create a whole other section of the game afterwards."

That's what playtests are for, of course: To highlight the uneven bits of an unfinished game. And from these tests, Valve discovered that something was missing in Portal.

"After much discussion, we settled on the idea that it was the lack of threat or pressure. Nothing in the game pushed back on the player. There was no real failure, no cost to mistakes, nothing overall to fear, no larger goal to strive for, and hence no real reason to advance," Walker said.

The team tossed around various ideas, but the idea of a central villain made the most sense. But not an overt one. Remember: The disembodied voice of GladOS is initially just guiding force. It's only over time that her sinister side starts to come out. That's really the sum total of Portal's story arc.

As it turns out, that was the whole idea.

"The antagonist [as we originally conceived it] could start as a narrative tool for introduction and reward," Walker explained. "Over time, [it would] become the thing that pushed back on the player, eventually giving them the core goal of the game."

GladOS is also just a voice for most of the game, and even that was dictated by Portal's development constraints. The game's art team was very small, so hinging the character's presence primarily on dialogue provided an easy solution to a logistical problem.

"players seem to start 'Portal' talking about the gameplay, but after they’re done, all they talk about is GladOS."

This is the secret sauce in game development, of course. There's no shortage of ideas in the world, but the trick is executing on those ideas using the technology, the resources, and the workforce that's available to you. It's unthinkable to imagine a Portal without GladOS, and yet she was only added to the game after a year of work had been completed, and for a very specific reason.

"In the end, there are many important decisions after this that were critical to GladOS working as well as she did, such as her entire personality," Walker said. "But her genesis begins with a straightforward process of us trying to solve the core gameplay problem in Portal.

"Even today, it’s always fascinating to us that players seem to start Portal talking about the gameplay, but after they’re done, all they talk about is GladOS."

There's much more to PC Gamer's interview with Walker and we highly recommend you take the time to check it out.