Once upon a time, Barney—Half-Life's lovable security guard companion—was a bad guy. Black Mesa's security guards were originally intended to be ineffectual, low level enemies, until a fateful AI test changed not only their role in the story, but the game as a whole. Valve programmer Steve Bond used an early version of Barney to run experiments in AI squad behaviour, with the player acting as squad leader. The idea was to stress test these computer-controlled characters' ability to navigate the game's complex levels. But seeing him in action made Valve realise that not every character in this secret research facility had to be hostile. Gordon Freeman could have friends.
In the earliest Half-Life prototypes, everyone wanted to kill Freeman. Every sentient being you encountered in Black Mesa, whether alien or human, was out to get you. But in the finished game, after Valve embraced the concept of friendly characters, he was able to recruit these security guards—collectively referred to as Barneys—to fight alongside him. The result of this happy accident is the best friendly NPC in the history of video games. Half-Life wouldn't be the same without these scrappy, quirky little weirdos, whose memorably eccentric dialogue and chaotic AI give them a tonne of character. Every firefight in the game is improved by having a Barney by your side.
In Half-Life 2, Barney Calhoun became a fleshed out character. But in the original game there are hundreds of him, scattered all over Black Mesa—and all with the same face and voice. It works, though. You somehow don't question the fact that the facility's security force is staffed entirely by clones. Despite their ubiquity, every Barney you meet is full of personality, thanks to a large pool of amusing, characterful voice lines recorded for pretty much any situation they might find themselves in. Actor Michael Shapiro (who also plays the G-Man) gives the character's voice a warm, folksy quality that's a perfect fit for the kind of Average Joe security guard Barney is supposed to be.
There are too many great Barney quips, observations, and one-liners to list here in full, but I love it when he kills a headcrab and calmly says "That's one less horror in the world." Confronted by a zombie he'll sometimes shout "Aim for the head! If you can find it..." Whenever he's doing particularly well in a firefight, excitement will get the better of him and he'll yell "Hah! Got another one!" like Luke Skywalker in the Falcon's gunner seat. There are some great idle lines too, like the classic "Catch me later, I'll buy you a beer." There's a nice callback to this in Half-Life 2 when a menacing Combine metro cop pulls off his mask, revealing Barney's smiling face. "Now, about that beer I owe ya."
Barneys get scared too. "I've got a bad feeling about this." they'll say nervously in certain areas, in another nod to Star Wars. It's also possible for Barneys to turn aggressive if you harm them or they see you killing a scientist. But not before a warning: "Step off, buddy!" or "I only take so much and no more." Valve recorded a ridiculous amount of dialogue for these NPCs, but their talkativeness, idiosyncrasies, and reactivity are a big part of what makes them so enjoyable to be around. The AI is completely rudimentary by modern standards, but it's amazing how every Barney you team up with feels like a little person—which makes their inevitable deaths extra unfortunate.
Run up to a Barney, hit E, and they'll become a loyal follower, firing at any enemies whose paths you cross. They're not the best fighters, and die very easily, but they can occasionally hold their own. Their 9mm pistol is weedy compared to Freeman's elaborate arsenal, but their range is superhuman, allowing them to occasionally kill HECU Marines that you've sufficiently softened up. They're hilariously fearless too, and will dash into battles they simply have no hope of winning—which only adds to their charm. Other shooters might have richer, more nuanced NPCs with smarter AI, but none of them are as effortlessly delightful as Barney, a true working class hero.