Update12/20/20: At the Disney Investors Meeting, Marvel announced that The Eternals would premiere Nov. 5, 2021. That's before December's Spider-Man: Far From Home sequel, but after July's Shang-Chi and the Legend of the Ten Rings.
Update 8/24/19: Marvel boss Kevin Feige confirmed at D23 Expo 2019 that Game of Thrones' Kit Harington, Captain Marvel's Gemma Chan, and Chernobyl's Barry Keoghan have officially joined the cast of The Eternals as Dane Whitman, aka the Black Knight, Sersi, and Druig, respectively.
Details about the upcoming Marvel movie were previously announced during a panel celebrating all things Marvel at San Diego Comic-Con. Feige revealed the star-studded cast of the film, which will be directed by Chloe Zha and will hit theaters on Nov. 6, 2020.
Game of Thrones and Bodyguard star Richard Madden will take on the role of Ikaris, the leader of the Eternals, a race of godlike beings tied to the very early beginnings of human evolution. He'll appear opposite Angelina Jolie as Thena; Salma Hayek as Ajak; Kumail Nanjiani as Kingo; Lauren Ridloff as Makkari; Brian Tyree Henry as Phastos; Lia McHugh as Sprite; and Don Lee as Gilgamesh.
Now, if you're wondering who the Eternals are, you're not alone. They're not as well-known as some of the other characters featured in the first three phases of the MCU. Created by the legendary Jack Kirby, the Eternals debuted in Marvel Comics in 1976. Their story is steeped in mythology, as they were created by the superior Celestials, immensely powerful and extremely old entities, through genetic experiments on the earliest forms of humanity. These experiments, which led to the possibility of super-powered mutation in humans, produced two races: the Eternals and their most frequent foes, the Deviants.
You can find out out more about the Eternals, their powers, and their history here.
Additional reporting by Megan Vick.