Non Playable Characters, also known as NPCs, are a core element that make many gameplay scenarios work and feel natural. The AI system of a video game has to be good enough to render credible scenarios populated with viable, lifelike characters that can act in an organic way as if they were living beings and not just lines of code. And because the most memorable characters are the ones with spunk, we made a list with 8 games that have the most unique and intelligent NPCs.
Left 4 Dead 2
The AI Director in Left 4 Dead 2 is optimized to keep track of the players’ progress and play style and adapt the difficulty levels accordingly. Thus, enemies such as the infected, will be spawned in specific areas and their combat skills and resilience will be boosted if the game detects that you are pushing too easily through them. Creating a customized gameplay experience for each and every player is one of the aspects that the AI Director excels at.
S.T.A.L.K.E.R.: Shadow of Chernobyl
S.T.A.L.K.E.R.: Shadow of Chernobyl is yet another gaming title known for its complex NPC AI that does not follow a specific pattern. Instead it is free enough to feel like it is truly alive. The complex artificial ecosystem featured in this game includes both wildlife and human NPCs who live in packs, defend their territories, explore, scavenge and have a personal life independent of both the main storyline and the player’s actions.
Destiny
Destiny is a very lively game and this is only possible with the help of its well well-defined NPCs that act in a natural, distinct way. As is the case with many other games developed by Bungie, the AI featured here has the power of evolving with the gameplay, the characters becoming stronger as the player advances and polishes his or her combat skills. It’s highly important to have NPCs that mix well with both the story and the mechanics and it seems that Destiny has this already figured out.
Grand Theft Auto Series
Players have always complained of how smart and well prepared the police forces from GTA are. It seems that they have a sixth sense that tells them where you are hiding, it becomes kind of easy to hunt you down and arrest you even if you lay low in the darkest of alleys. In addition to this, setting spike strips on the road, boxing you in with two Police cars and monitoring the area from their helicopters are some other spot on tactics that are very hard to trick.
Alien: Isolation 
The Xenomorph’s A.I. is truly something to feast your eyes on. Almost totally unpredictable, it can pop up anywhere and it really knows how to play a constant cat-and-mouse game. What is even more impressive is that it can adapt to the player’s tactics as the gameplay advances, becoming more dangerous as you progress through the levels. The Xenomorph can learn to pick up even the slightest noise you make so it becomes almost impossible to avoid his gaze.
The Last of Us
The enemy NPCs in The Last of Us are some of the best ones that you can find in a video game. Highly intelligent and with a natural behavior, they are able to perform each and every action the player can, making it so much harder to beat them. But fear not, because you have Ellie, the best, most humanized companion NPC, who will take cover to help you protect her and will even attack enemies who have you pinned to get them off of you.
Bioshock Infinite
Elizabeth is such an independent and lively NPC that a lot of times it feels like she’s the real hero of the story. Extraordinarily intuitive and helpful, she is highly intelligent and helps Booker countless times, throwing him useful salts, ammunition and opening up tears in space-time to help him fight off enemies. Elizabeth has such an effervescent presence, she compensates for a thousand other NPCs, building up the storyline in a very natural way.
Half Life Series
Half Life is a highly-esteemed game that is still a fan favorite even after 20 years since its release and the AI that shapes the gameplay is one of the best aspects it features. When players first got their hands on the game, they had their minds blown by the insightful NPCs and flexible, hard-to-beat enemies that really stepped up the game in terms of combat mechanics. The fondest memories of many gamers are surely linked to Half Life and the intense hours spent beating up Combine soldiers.