Those who expelled Kang to the quantum realm are likely to become the next major adversaries for the Avengers in the future of the MCU.
The next major antagonist of the Marvel Cinematic Universe (MCU) has officially stepped onto the big screen through the blockbuster Ant-Man & the Wasp: Quantumania. In this film, Kang is imprisoned in the quantum realm and needs the assistance of Ant-Man Scott Lang to escape and continue his ambition of conquering the multiverse.
Moreover, those who banished Kang to this strange world are actually variants of himself from different realities, fearing that he would overthrow them to become the sole entity in the universe. These variants even establish an organization with countless members called the Council of Kang, holding many secrets of the Marvel multiverse.
The Council of Kang in the MCU

The Council of Kang makes its official appearance in the mid-credits scene of Ant-Man & the Wasp: Quantumania, and is also the organization that banished Kang to the quantum realm. The name says it all; this organization consists of hundreds of thousands of Kang variants from countless timelines, with its main headquarters being a mysterious arena yet to be revealed.
Leading the Council of Kang is a variant known as Immortus, often appearing in the source material as a multiversal antagonist. His most formidable weapon is his ability to manipulate psychology to become the supreme ruler of the end of time, akin to the role of He Who Remains in the series Loki.
In addition to Immortus, the Council of Kang is also governed by Rama-Tut - Kang's Pharaoh variant from ancient Egypt. In the comics, Rama-Tut has been an adversary of the Fantastic Four and even faced off against En Sabah Nur - Apocalypse, the first mutant in Marvel history. Although Rama-Tut has returned to the future, he sometimes traverses through time to trouble the Avengers in their own comic storylines.

Finally, alongside Immortus and Rama-Tut, there is another peculiar variant of Kang. Visually, this could be the Scarlet Centurion, with a body integrated with futuristic high-tech armor. In the source material, this armor allows him to freely traverse through time and enhance himself, thereby becoming a formidable foe for many powerful superheroes.
In the mid-credits scene of Ant-Man & the Wasp: Quantumania, the Council of Kang has decided to convene after Kang the Conqueror's demise to discuss the threat posed by the Avengers in the Earth-616 universe. With Ant-Man having slain Kang, coupled with superheroes like Doctor Strange and Spider-Man meddling with the time stream, the Council's plans for the multiverse are jeopardized, forcing this organization to take action.
The Council of Kang in Marvel Comics

The Council of Kang made its debut in 1986 through the comic issue Avengers #267. Leading this organization is Prime Kang, who harbors ambitions to eliminate all lesser or divergent versions of himself. However, this is actually part of Immortus's plan to shape Prime Kang's future according to his own desires.
The Council of Kang comprises numerous variants of Kang from the multiverse, handpicked by Prime Kang to serve his conquest plans. With each variant defeated, he seizes a new reality, gradually constructing his mighty empire. However, as previously mentioned, it's all part of Immortus's scheme, aiming to sow discord and provoke Kang variants into slaughtering each other.

The most significant difference between the cinematic Council of Kang and the original lies in the leadership position. Immortus openly leads this organization instead of acting as a puppet master behind the scenes. Additionally, Prime Kang does not appear in the mid-credits scene of Ant-Man & the Wasp: Quantumania, and it's unclear if he is a member of this organization. However, it's not ruled out that Marvel Studios might be concealing the identity of another Kang variant, secretly manipulating other variants before officially revealing in the next Avengers blockbuster.
Furthermore, the motives and actions of the Council of Kang on the big screen have been somewhat altered compared to the source material. Although Immortus still seeks to defeat and eliminate any variants daring to oppose him, such as Kang the Conqueror, he seems to have no intention of inciting a civil war among the Kang variants.
Instead, this motive has been shifted to He Who Remains, who once manipulated the multiversal war to eliminate all timelines except Earth-616. That's why after this character's departure, the Marvel multiverse was freed, restoring freedom to other variants. The ultimate goal of the Council of Kang, up to the present moment, is to maintain the organization's position in the multiverse and of each member in their respective realities.
The Role of the Council of Kang in the MCU

With the announcement of projects in phases 5 and 6 of the MCU, Marvel Studios indirectly confirmed Kang's significant role in the fifth Avengers blockbuster - The Kang Dynasty. However, since The Conqueror variant met his demise in Ant-Man & the Wasp: Quantumania, it's highly likely that the new Council of Kang will be the next major adversary that the Avengers must confront.
Marvel Studios may need to find a way to narrow down the scale of this battle, as the Council of Kang has numerous different members, and exploiting all of them on the big screen is almost an impossible task. Since the mid-credits scene of Ant-Man 3 focuses only on Immortus, Rama-Tut, and Scarlet Centurion, these three variants are likely to be the main antagonists in The Kang Dynasty and will directly attack the Earth-616 timeline, threatening the existence of all other realities as well as the balance of the multiverse.
Previously, the Council of Kang is likely to return in season 2 of the Loki series, featuring the variant Victor Timely. Additionally, Marvel Studios is also developing numerous projects related to multiverse elements or time travel - all great opportunities for them to delve deeper into their next major antagonist. This includes Deadpool 3, with Deadpool and Wolverine coming from another reality; or Fantastic 4, where Rama-Tut could confront the Fantastic Four similar to the comics.
Furthermore, Kang variants are almost certain to appear in Avengers: Secret Wars - the project concluding phase 6, as well as the MCU's multiverse storyline. This blockbuster will directly connect with The Kang Dynasty, like two chapters of the same story, akin to Infinity War and Endgame before.
Sources: Marvel Studios, ScreenRant