How GLaDOS solved one of Portal's biggest problems

The Orange Box is a decade old, but it only seems like yesterday that Valve's five-game compilation, which included Half-Life 2 and its two continuations, Episode One and Episode Two; Team Fortress 2; and Portal, was hitting shelves. 

It's strange to think that, back then, Portal was something of a mystery. Half-Life was still going strong (those were the days) and Team Fortress had already amassed a following, but no one had any idea what to expect from the quirky, reality-bending puzzler. Not even Valve. 

Despite being an unknown quaniity, Portal soon became the talk of the town. And while the portal-flinging mechanics were truly special, it was the game's robot antagonist, GLaDOS, that emerged as the star of the show. 

Now, in a recent interview with PC Gamer, Valve designer Robin Walker has explained how the cake-loving maniacal machine came to be. 

"In any game's development, there are too many decisions to count, and many of them will ruin the game if made incorrectly," says Walker. "One decision that ended up being very important was the one behind GLaDOS."

Walker recalls how after a year in development, the team had 14 levels ready for playtesting. There was, however, no GLaDOS, and players moved from puzzle to puzzle without any real sense of narrative progression or reward. 

Playtesters still responded positively to that GLaDOS-free experience, but many kept asking "when does the game start?" Without any story beats to hit or emotional adversity to overcome, most felt the core levels were tutorial missions leading to something bigger. That's when Valve became worried. 

"Considering the entire game was really just a process of learning about the core gameplay mechanic, this scared us a lot," continues Walker. "We talked about various solutions, and in the end decided that introducing an antagonist made the most sense.

"The antagonist could start as a narrative tool for introduction and reward, and over time become the thing that pushed back on the player, eventually giving them the core goal of the game. We had little in the way of art production on the team, so it being a character that largely spoke to you via voice over was a straightforward production solution.

"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. But her genesis begins with a straightforward process of us trying to solve the core gameplay problem in Portal."

The full interview goes into more detail and is well worth a read. Check it out over on PC Gamer.