Galactus

Galactus had already shown up on the big screen in Fox's Fantastic Four: Rise of the Silver Surfer (2007). There he barely has a shape: he's a huge cosmic cloud closing in on Earth, guided by the Surfer's board. In the end, the Surfer turns on his master and hurls himself at him to save the planet. The giant, helmeted version from the comics was left out.

In The Fantastic Four: First Steps, the story takes place on Earth-828, in a retro-futuristic 1964. The Fantastic Four are celebrating four years together and Sue Storm finds out she's pregnant. That's when the Silver Surfer appears in the sky and announces that the planet has been chosen to be devoured by Galactus.

The team heads into space after him and sees the Devourer of Worlds in action, consuming another planet. Galactus appears as the giant from the comics, in armor and helmet, played by Ralph Ineson. He captures the team and notices something not even the parents fully knew: the baby Sue is carrying has enormous cosmic power.

Galactus offers a deal: he'll spare Earth if he gets the child. His hunger is eternal, and he sees in Franklin someone who could inherit that burden. The Fantastic Four refuse and escape. Sue gives birth to Franklin during the escape, and they use a neutron star's gravity to shake off the pursuit.

Back home, Reed tells the world the truth and public opinion turns against the family: plenty of people think handing over a baby is an acceptable price. Sue promises she won't give up her son or abandon humanity.

The first plan is to move the entire planet away using a network of teleportation bridges built with help from several countries. The Surfer destroys almost all of them. One is left, and the plan changes: use Franklin as bait to lure Galactus to him and send him far away through the portal.

Nothing goes as planned. Galactus sees through the trick and grabs Franklin. Sue, pushing her force fields to the limit, shoves the giant toward the portal while Reed rescues their son. Johnny tries to sacrifice himself, but the Surfer stops him: he had already discovered she is Shalla-Bal, from Zenn-La, who became a herald to save her own planet. She throws Galactus through the portal herself and goes with him, to a distant point in space.

Sue passes out and seems dead, but Franklin touches her and she starts breathing again, the first clear sign of the power Galactus wanted.

Galactus debuted in 1966, in the three-part saga in Fantastic Four #48 to #50, by Stan Lee and Jack Kirby. In the comics he was Galan, a mortal from the planet Taa who survived the end of the universe before ours and was reborn as a force that must devour worlds. The classic herald is Norrin Radd, the Silver Surfer, and Shalla-Bal is his beloved on Zenn-La. In the film, Marvel merged the two figures into one.