Players have a special relationship with their characters. We spend days in their shoes, experiencing their joys and hardships. You will make choices as them and shape the world around you. It's this same relationship, though, that can make a protagonist a compelling villain.
Some of our favorite main characters fall from grace in between games. Often times, it's the events of that previous game that shape them into who they become. This insight into their development and motives makes them extremely empathetic, no matter how downcast they've become, or how badly they need stopped.
10 The Soul Of Cinder: Dark Souls 3
The Soul of Cinder, which guards the First Flame, is an amalgamation of every player character to ever kindle the fire, though it hardly comprehends its position. A mindless, duty-bound suit of armor is all that remains after untold eons of battle. It's unaware of the pain and suffering caused by the flame it protects.
The Soul of Cinder is unique in that you might not consider it a villain, depending on how steeped in Dark Souls lore you are. Every time you unconsciously rekindled the First Flame, you unknowingly prolonged an era in permanent decay. Every one of us had a hand in this monster's creation.
9 Kazuya Mishima: Tekken
Kazuya may be the protagonist of the first Tekken, but he's never been a hero. Kazuya spends his first outing on a quest for vengeance. This masks his true nature, as he promptly spends the rest of the series attempting to run an evil organization and starting fights with anyone in his gene pool.
Kazuya's role as a villain would fluctuate over the years, but he never lost his soft spot for throwing his father off a cliff. He's also come to a mutually-beneficial agreement with the demon inside his heart, but he no longer tries to kill his son. So, call him an anti-hero now?
8 Caim: Drakengard
Drakengard is a complicated series. It has a non-canon sequel and a joke ending that leads directly into the Nier universe. In both of these situations, the protagonist of Drakengard, Caim, becomes a villain. In Drakengard 2, Caim aims to destroy the seal holding the world together to free his friend. There were steps to replace the seal instead, but he was angry enough to not care.
In the Drakengard ending that leads to Nier, it's heavily speculated that Caim becomes the Legion leader, Red Eye. If this is true, this would make him the general for the very being he fought to destroy.
7 Talion: Shadow Of Mordor
Talion is a completely original character to the Lord of the Rings universe. This opened the door for him to be whatever the writers wanted him to be, and they would choose to make him instrumental in the history of Middle Earth. Talion would retake parts of Mordor, wear a Ring of Power, and defeat Sauron. Not bad for an OC.
Talion is such a good character that it's heartbreaking, and admittedly awesome, watching him accept a Ring of Power. This seals his fate as he slowly turns into a Ring Wraith. While we never face Talion personally as a villain, his battles are technically featured in the films.
6 Red: Pokemon
Angsty and bitter may be the loosest definition for a villain, but it counts for Pokemon, and it's Red's attitude that really makes him feel like a bad guy. In Gold, Silver, and Crystal, he's lost all motivation and hope for Pokemon battling. It's nothing more than a predictable tic-tac-toe game to him now.
This stands in the face of the players love for the game. Our love of Pokemon is being belittled by this jaded child. That's why he's a villain. He needs a harsh pep talk, and we're happy to do it. Thankfully, he looks a lot happier by Sun and Moon.
5 Arthas: Warcraft
Arthas is the truest definition of a tragedy. He is a high-born hero, built by expectations and providence, and who falls due to his own hubris. Warcraft 3 takes its time making you watch Arthas stumble towards villainy, and because of his birthright, he believes in his goals with absolute certainty.
This culminates in a brutal act of patricide, and by the time of World of Warcraft, Arthas is threatening war on the entire planet. He truly is the poster child for "maybe the Alliance are the bad guys."
4 Prince Aidan: Diablo
Diablo has surprisingly dense lore for how little is explained in game. The protagonist of Diablo was originally nameless and without a background, until Diablo 2 and 3 fleshed out the story. As it turns out, the prince of Tristram, Prince Aidan, was responsible for sealing the ancient evil.
Diablo's Soulstone slowly takes over Aidan's body, however, and by Diablo 2, he is transforming into the Lord of Terror. Whether or not you actually consider Aidan the villain in this scenario, he does still drag demons in his wake while conscious of his actions.
3 Revan: Star Wars
Revan is a good guy, turned bad guy, turned good guy, turned neutral, turned bad guy. That's quite the resume. Part of this is probably because writers just can't keep their hands off him. He's so iconic that he was brought back for The Old Republic MMO, where he should be 300 years dead by now.
It's here though, where he's finally approached as a confrontable villain. After being tested by the universe one-to-many times, Revan decided, "heck it," and chose to blow everyone up equally.
2 Naked Snake/Big Boss: Metal Gear
Naked Snake technically begins as an undercover villain in the first two Metal Gear games, but people remember him best for his rookie outing in Metal Gear Solid 3. This is the mission that broke him and led to his decline. He never lost his optimism, but acting on it became harder as he was betrayed time and time again.
Snake originally conceived of a world where soldiers would always have a home; where they wouldn't just be tools, and where they could stand as a deterrent for the entire world. When people wanted to fight, they could fight Big Boss. Only, as time went on, Big Boss' dream turned into a full-fledged war economy.
1 Mario Jumpman Mario: Donkey Kong
Mario is a villain, and here's why. What is Mario's goal in the original Donkey Kong? To save the princess, right? But what does he do with the bad guy once he defeats them? Well, in Donkey Kong Jr, it turns out he captured Donkey Kong, imprisoned him, forced him to perform circus acts, and assaulted his child for trying to rescue his father.
In Donkey Kong Jr, Mario spends his hours throwing objects and animals at a defenseless gorilla who's just trying to save his daddy. Keep in mind this literal baby has no idea why its father is in prison. Mario is simply punishing this infant for nothing other than wanting parental security.