WARNING: Spoilers for Spider-Man: No Way Home and all Phase 4 movies and television series released in 2021
Even though the Marvel Cinematic Universe is only a year into Phase 4, there have already been some major character deaths. Many of these deaths are already having a significant impact on the MCU, with others poised to have an extensive impact in upcoming movies and television series.
Some of these characters debuted in the Infinity Saga or are variants of familiar characters, while others are new characters introduced in 2021 and died in the same stories they were introduced in.
Dreykov
Dreykov is one of Phase 4's weaker villains so far, yet his death is still an important one. The death of Dreykov ensures the end of the Red Room and that all of the Black Widows under his control are now free.
This opens the door for former Black Widows other than Natasha Romanoff and Yelena Belova to make an impact on the MCU now that they are free to make their own choices and use their skills as they desire. The end of Dreykov also brought some much needed closure for Natasha and Yelena.
Gilgamesh
Gilgamesh was one of the most likable Eternals. His death at the hands of the Deviant Kro devastated the Eternals. It showed that there were real consequences and that despite their powers and longevity, the Eternals were not invincible.
When Gilgamesh died, he told Thena to remember his words. This is a reference to defending what you love at all costs. Thena passed these words onto Sersi, which helped convince Sersi to become the leader of the Eternals and stop the birth of the Celestial Tiamut in order to save Earth and its people.
Derek Bishop
Derek Bishop died owing a lot of debt to Wilson Fisk/Kingpin. Kingpin used this debt to blackmail Eleanor Bishop into doing all kinds of dirty work in order to pay off her husband's debt. Her relationship with Kingpin is what brought the iconic villain into Hawkeye and the MCU.
Derek's death influenced his daughter Kate Bishop to become a hero. She wanted to honor her father by being fearless and helping people like he did. With Kate becoming one of the MCU's most important heroes and Kingpin likely becoming one of the most important villains, Derek's death will continue to impact Phase 4.
William Lopez
Flashbacks in Hawkeye showed William Lopez as a loving and supportive father of Maya Lopez before his tragic death at the hands of Ronin. His death fueled Maya's vengeful hunt for Ronin in Hawkeye, until she learned that her "uncle" Kingpin and her good friend Kazi betrayed William and engineered his death at the hands of Ronin.
This traumatic revelation motivated Maya to leave Kingpin's empire. She killed Kazi and also put a gun to Kingpin's head and pulled the trigger. Maya's pursuit to get justice for her father's death will definitely factor into the upcoming Echo series on Disney+ and as Kingpin inevitably continues to expand his villainous reign in the criminal underworld.
Christine Palmer
A lot of characters died in What If...?, but Christine Palmer's death is the most important in that series because it seems poised to impact the wider MCU. In the show's fourth episode, Christine is killed in a car accident with Stephen Strange. Desperate to undo her death and prevent it from happening, Strange goes down a much darker path than in the movies and becomes Strange Supreme.
No matter what he does or how powerful he becomes, he can never save her as her death is a fixed point in time in that universe. The trailer for Doctor Strange in the Multiverse of Madness appears to show Strange Supreme, teasing that he will have a major impact on the multiverse chaos and the main story of the MCU. The creation of Strange Supreme would never have happened if not for Christine's unavoidable death and the lengths it drove Doctor Strange to in What If...?.
Maria Rambeau
Flashbacks in WandaVision revealed that Maria Rambeau passed away from cancer during the Blip. As the founder and leader of S.W.O.R.D., the direction of the organization changed drastically after her death when Tyler Hayward took over. He used the organization's resources and influence to serve his corrupt agenda.
In addition to the direction of S.W.O.R.D., the death of Maria had a profound impact on her daughter Monica. After being Blipped for five years, Monica suddenly returned to learn that her mother passed away, even though the last time Monica saw her, she was doing better. Monica's grief and the lack of closure allowed her to understand what Wanda Maximoff was going through with Vision's death, an understanding that allowed Monica to reach Wanda and empathize with her in a way that no one else could. The death of Maria Rambeau will also definitely continue to impact Monica in The Marvels.
May Parker
The Green Goblin's murder of May Parker had a devastating effect on Peter Parker. Her tragic death nearly sent the normally hopeful Spider-Man down a dark and vengeful path that he would never be able to recover from. If not for the intervention, wisdom, and guidance of Tobey Maguire and Andrew Garfield's Spider-Men, the MCU's Peter Parker could've gone down a worse path than any live-action Spider-Man has ever gone down.
Beyond the personal impact on Peter, the loss of Aunt May had a larger impact on the MCU and the future of Spider-Man. Her sacrifices and the fact that he had to live without his last family member and the woman who raised him influenced Peter's decision to have everyone forget who he is and that he is Spider-Man. If not for May's death, Peter probably would not have made this bold and game-changing sacrifice.
Xu Wenwu
Xu Wenwu was an influential and powerful warlord for over one thousand years. He frequently changed the course of human history through wielding the Ten Rings and through the work done by the Ten Rings criminal empire.
With Wenwu sacrificing his life to protect his family from the Dweller-in-Darkness, both the actual Ten Rings and the Ten Rings criminal empire are about to go down a new path. Wenwu's son Shang-Chi is in possession of the Ten Rings and his daughter Xialing now leads his empire. The Shang-Chi post-credits scenes tease the importance and mystery for both these things in the future of the MCU, a future left uncertain and more important than ever after Wenwu's death.
Ajak
Ajak's death forever changed the mission of the Eternals. Under Ajak's leadership, the Eternals spent thousands of years on Earth influencing the progression of humanity for the Emergence of the Celestial Tiamut. Ajak had a change of heart and wanted to save the people of Earth from the destructive Emergence. Despite her death, Ajak ensured that Sersi would be the next leader of the Eternals instead of Ikaris. Ajak's death also brought the Eternals back together after spending centuries apart.
Through their reunion and under Sersi's leadership, many of the Eternals banded together to stop the birth of Tiamut, thus saving the Earth and all of its people. All of this had an impact beyond Earth and set up an important plotline for Phase 4 as Arishem the Judge was angered by the Eternals preventing the birth of a Celestial. Arishem's judgment and how he responds to their actions could impact the survival of Earth and planets all over the universe.
He Who Remains
He Who Remains is easily the most important death so far in Phase 4. When Sylvie kills him in Loki, she brings about the end of the Sacred Timeline and unleashes the dangers of the multiverse and the more dangerous variants of He Who Remains.
His death is consequential for everyone in every single reality. The chaos unleashed by his death is only getting started and is already being felt in many MCU stories. It will get even worse with Kang the Conqueror being free, along with the other variants He Who Remains was keeping at bay.