Milo James Thatch (or Milo) is the protagonist in Disney's 2001 animated feature Atlantis: The Lost Empire. He is also half of the animated supercouple Milo and Kida. He is voiced by Michael J. Fox in the film, and by James Arnold Taylor in the direct-to-video sequel Atlantis: Milo's Return.

Milo is a linguist (though employed by the Smithsonian Institution to mind the boilers), grandson of scientist and explorer Thaddeus Thatch. Like his granddfather, he hopes to find the lost city of Atlantis. Preston Whitmore, a friend of his grandfather, he is given the Shepard's Journal, which contains information about Atlantis. Whitmore hires an expeditionary team to help Thatch find the lost city.

In Atlantis, Milo befriends the citizens and gains their trust, although the king remains skeptical. Milo particularly befriends Princess Kidagakash, who becomes the film's love interest. Kida and Milo discuss how Atlantis came to its present underwater state.

After a research mission, Milo finds himself threatened by the members of his team, who are interested only in the money to be gained by acquiring the legendary Heart of Atlantis, not in research. Milo refuses to join them, and they kidnap Kida. Milo at first refuses to help them find the Heart of Atlantis, knowing that it is the life source for the city. When Rourke threatens to shoot Kida, however, Milo accedes.

In the underground chamber where the Heart of Atlantis sits, Kida becomes one with it; it is then locked up in a container and loaded onto a truck. As they prepare to leave, Milo attempts to persuade them what they are doing is wrong. He convinced all but Rourke, the team's leader. When Rourke and knocks him to the ground, the team has a change of heart, and goes to help Milo up and stand at his side, with the exception of Rourke's mercenaries. Helga Sinclair, ever loyal to Rourke, stays on his side and leaves with him. The elderly king asks Milo to save his daughter on his death bed.

Milo and several residents of Atlantis use flying machines pursue Rourke and Helga, who have attached the container holding Kida and the Heart of Atlantis to a hot air balloon; they are prepared to leave through the caldera of the dormant volcano above Atlantis. A lengthy air battle ensues; Milo and Rourke confront each other individually. An axe that Rourke swings breaks the window of the container that holds Kida. Milo grabs a piece of the broken glass and cuts Rourke's arm. Because the glass was covered with energy from the Heart, this cut turns Rourke into a glass monster. While trying to go after Milo again, he is caught in the propellers at the bottom of the balloon and shatters.

Milo detaches and rescues the container as the balloon crashes. The balloon's crash also reactivates the volcano. Kida, still bound to the Heart of Atlantis, awakens large moving statues to form a protective barrier around the city. She then rises into the sky and returns as her ordinary self.

Milo decides to stay with Kida in Atlantis while the others return to the surface, all extremely wealthy, and keeping everything that happened a secret.

In the final scene, we see Kida, now as queen, and Milo completing the carving of the newest ancestral stone to honor Kida's father. The film ends as the two then climb to the top of a building together and watch the stone rise into the sky above the city.

In the sequel, Atlantis: Milo's Return, Milo and Kida meet back up with the remaining team (all except the now deceased Helga and Rourke) and return to the surface, to investigate various happenings in the (seemingly more modern) world.