Loki was one of the oldest villains in the MCU. First appearing in Thor, he would go on to become the main antagonist in The Avengers before having subsequent appearances in Thor: The Dark World and Thor: Ragnarok. Throughout his time on-screen, Loki went through a redemption arc of sorts where he went from the God of Mischief to someone proud of his Asgardian and Jotun heritage, fixing his relationship with Thor.
That said, Loki did a lot of awful things before his untimely demise in Avengers: Infinity War. We're looking back at the 10 worst things Loki has done so far.
10 UNLEASH THE HULK
Loki knew that he couldn't outmatch Earth's Mightiest Heroes in The Avengers, so he came up with a plan to subdue them. This included getting captured and imprisoned on the Helicarrier so that he could unleash the Hulk.
His plan was successful, making Bruce Banner's and the rest of the team's worst fears come true. Not only did Hulk nearly destroy some of the other Avengers, but almost wrecked the entire Helicarrier by himself. Many SHIELD agents' lives were placed in danger, all because the Hulk was let loose. If it weren't for Thor also being on the ship, the results would've been much worse.
9 DESTROYED PHIL COULSON
While we take the crossover-centric MCU for granted, that was just a pipedream back in Phase One. There was one character that seemed to tie the team together, which was SHIELD agent Phil Coulson. Coulson appeared in Iron Man, Iron Man 2, and Thor, having a hand in most of the founding Avengers. He was also ecstatic to meet Captain America and see the team formed to help save the world. Unfortunately, Loki's invasion of the Helicarrier would be curtains for him. This noble agent was cut down by the God of Mischief in a matter of seconds, leading the Avengers to unite.
8 USURPED ODIN
While Loki seemed to be on a better path in Thor: The Dark World, the end of the film proved that he was up to his old tricks. After faking his own death, he managed to usurp the throne of Asgard and banish Odin to another realm. This meant that Asgard was under the command of Loki from Thor: The Dark World all the way to Thor: Ragnarok. Usurping Odin also caused the Allfather to essentially be trapped on Earth and stripped of his power in the process. It was Loki's actions here that started the events of Ragnarok, which led to the destruction of Asgard.
7 LED THE DARK ELVES TO THE PALACE
At the end of The Avengers, Loki was taken back to Asgard by Thor and placed in a prison for years. In Thor: The Dark World, Loki remained in confinement, having brief moments of conversation with his old family and friends. However, he was still not meant to be trusted, which was proven when the Dark Elves came knocking.
While Kurse was letting the prisoners free, Loki told him the directions to the palace so that he could confront Odin. Unfortunately, this move backfired on Loki, as it resulted in the death of his mother, Frigga, the parent that he was close to.
6 NEARLY DESTROYED JOTUNHEIM
In Thor, Loki was jealous of his brother's place in Asgard. They were both in line for the throne, but it was ultimately Thor who was chosen to take his father's place. This sent Loki spiraling, which caused him to come up with a plan to become worthy of the throne. He tried to destroy Jotunheim, a realm that fought with Asgard several times, by leaving the Bifrost open. There are shots of the realm's structures falling and many of the Frost Giants running away in terror. Keep in mind that this was after Loki tricked Laufey, the king of the Frost Giants, and cut him down.
5 SNUCK THE TESSERACT
At the end of Thor: Ragnarok, it seemed that Loki had finally joined his brother in fighting the good fight. However, he was still up to his old tricks. While he was resurrecting Surtur in Odin's Vault, he came across the Tesseract, which he used in The Avengers to try and take over New York. At the start of Avengers: Infinity War, it was confirmed that Loki, indeed, took the Tesseract for himself. It wasn't clear what he planned to do with the Infinity Stone, but it was all for naught. It was his greed that began the Mad Titan's quest for genocide.
4 TRIED TO KILL THOR
Thor was banished to Earth in his first movie to learn humility so that he would be a better leader. At the climax of the film, Loki sent the Destroyer to make sure that his brother didn't come back to Asgard. Thor, with no powers, had to work with the Warriors Three to try and destroy the machine. His final strategy was self-sacrifice in an effort to save his friends, which Loki gladly took him up on. The Destroyer backhanded him, leaving Thor for dead. However, that was precisely the move that made the God of Thunder worthy of Mjolnir again.
3 INVADED NEW YORK
Loki was the villain of The Avengers, meaning that he did a lot of awful things in that movie. He slaughtered people in Germany, sent the Hulk on a mad rampage, and even took over Hawkeye's mind. His crowning achievement was his invasion of New York with the Chitauri army, though.
Opening a portal, he had legions at his command, all trying to destroy the city and take down as many people as possible. Loki's actions here caused a lot of damage in the MCU as a whole. People weren't the same after that, and their lives was changed forever.
2 LED ASGARD TO COMPLACENCY
Four years passed between the events of Thor: The Dark World and Thor: Ragnarok. That means four years went by since Loki took over Asgard under the guide of Odin. That was a long time to wonder what was happening to the city under Loki's leadership. At the start of Thor: Ragnarok, we see that the God of Mischief had led Asgard to complacency, putting on ridiculous displays and erecting statues in his honor. Asgard had lost its touch because of Loki, not helping to protect the Nine Realms. Thor was the only one trying to save the Nine Realms as a result.
1 TRIED TO STRAND THOR
It seemed that Loki and Thor were finally reaching a mutual understanding in Thor: Ragnarok. After having a meaningful talk, they were working together to get off Sakaar. However, Loki was about to take the opportunity to strand his brother and call the authorities on him.
This would not only doom Asgard and everyone on it, but doom Thor to confinement by the Grandmaster for the foreseeable future. Thankfully, Thor was already onto Loki and had a backup plan prepared. He shocked Loki with the technology Valkyrie used and left him there for the rest of the champions to find.