Galactus was chosen as the main antagonist of Lego Marvel Super Heroes.
The 2013 action-adventure game uses an original Marvel story rather than adapting one particular film. Doctor Doom and Loki assemble villains and pursue Cosmic Bricks, fragments of the Silver Surfer’s shattered board, in an attempt to control enormous cosmic power.
Galactus is the game’s ultimate threat because he arrives intending to consume Earth. Loki manipulates him through a control device, while the heroes and villains eventually form an uneasy alliance to stop both of them. That plot role is why Galactus, rather than Doctor Doom or Loki, is the canonical answer.
The distinction can be confusing because Doctor Doom and Loki drive much of the scheme and serve as major recurring villains. Galactus, however, is explicitly identified as the main antagonist and becomes the climactic danger. The game features 180 playable Marvel characters, 15 main campaign missions, and versions of locations such as Manhattan, Asgard, Liberty Island, and Ryker’s Island.