Before Thanos snapped half of the life in the galaxy out of existence, he also personally killed several Avengers: Infinity War that he was properly debuted in his full, menacing, glory.
With a limited time to establish the Infinity Saga's overall villain, directors Joe and Anthony Russo told the story of Infinity War mainly from Thor's perspective. This kept the film's focus on the villain, effectively making him the main character of the narrative. After years of waiting on the sidelines and a couple of failed attempts to secure the Infinity Stones, he finally took it upon himself to seek the gems. The difference with Thanos from most MCU villains is that he's not inherently bad. His actions were motivated by his unwavering belief that to be able to keep the universe sustainable, it had to be balanced by random genocide. Granted that it's a twisted way of looking at the situation, highlighting his messiah complex, Infinity War presented the Mad Titan as an empathetic villain.
While Thanos caused the death of countless creatures in the galaxy, he, interestingly, didn't go out of his way to kill anyone. That doesn't mean, however, that he didn't personally murder some who got in his way. Here are all of the characters that the Mad Titan personally killed in the MCU.
Heimdall
The ending of Heimdall transported the Hulk out of the ship and into the Sanctum Sanctorum where Bruce Banner encountered Doctor Strange for the first time. Since this was an attempt to derail his plans, Thanos took it upon himself to make Heimdall pay; using the character's own sword, he stabbed him in the chest, killing the character.
Loki
With his unsuccessful attempt to take over Earth, not to mention losing both the Space and Mind Stone in providing him with the Mind Stone. But after the Avengers foiled his plans, Loki never got the chance to make up for his mistakes against Thanos. Their reunion in Avengers: Infinity War was never going to be pretty, with the villain demanding that Loki give up the Tesseract he swiped from Odin's vault in Asgard. Pretending to play along, Loki attempted to deceive Thanos into believing that he could still be trustworthy and useful for his overall plan, then he tried to kill Thanos with his dagger. Unfortunately, the Mad Titan was fully expecting him to pull that move, catching the God of Mischief by the throat and choking the life out of him.
Gamora
Unlike his first couple of personal kills in Avengers: Infinity War, Thanos murdering Gamora was very difficult for the Mad Titan. While the villain had adopted many children during his quest to balance the universe, he was particularly fond of the Guardians of the Galaxy member, Gamora. Sent to locate the Soul Stone, she was forced to give up the information to save her sister, Nebula, whom Thanos was using as a hostage. Upon learning about where the Infinity Gem was, the father and daughter went to Vormir, not knowing that acquiring the crystal required a sacrifice of something one genuinely loves.
Initially, Gamora didn't realize the danger she was in, not knowing that Thanos actually loved her. She even started to mock her adoptive father, assuming that this was the end of his maniacal mission. Realizing that she was the perfect sacrifice, Thanos heartbreakingly dragged her to the edge of the cliff and threw her to her death.
Vision
As the holder of the Mind Stone, Vision automatically had a target on his back when Thanos started actively seeking the Infinity Stones. His safety became the primary mission for the Earth-based heroes in Avengers: Infinity War, leading them to Wakanda where Shuri attempted to extract the Infinity Stone safely from his forehead. Unfortunately, with of the Black Order and the Outriders fighting hard to take over Wakanda, they were left with no time to move forward with the procedure. In the end, Wanda tragically had to destroy the Mind Stone from Vision's forehead, killing her lover in the process. But, that wasn't the end of Vision: with Thanos already armed with the Time Stone, he simply reversed time before the Mind Stone was still intact and plucked it out of Vision's forehead, leaving a massive crack on his forehead, effectively killing him twice.
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Among these characters that Thanos personally killed, however, three of them are already slated to return. Loki and Gamora will appear in the Vision will be on WandaVision opposite his lover, Wanda. It's still uncertain how he's able to be back with the Mind Stone, but the Disney+ series is expected to provide some answers. It's also worth noting that aside from these Marvel Cinematic Universe, Thanos also attempted killing Iron Man, but Doctor Strange's intervention saved him.
