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- "A hero is more than a person, a hero is a belief. A belief that, against impossible odds, the world can be saved—and that the world is still worth saving. Heroes inspire that belief in us. They renew our faith and give us that most precious of all gifts—hope. The world needs heroes. That's why, when a true hero arrives, the world will honor him."
- —Xbox.com introduction of "Believe".
Believe is a Microsoft marketing campaign for Halo 3 produced by New Deal Studios. It features the word "Believe" as a tagline, and appears to be honoring the legacy of SPARTAN-117, citing him as a hero of the United Nations Space Command whose brave actions inspired other servicemen during the Human-Covenant War.
It includes handouts, live-action TV commercials, magazine page advertisements, and XBOX live marketplace ads:
- Believe - A pamphlet distributed at the Project Revolution musical festival, featuring in-universe musical presentation of the UNSC Symphony Orchestra.
- Diorama - An interactive flash movie, a part of the Believe campaign for Halo 3. It is a fly through of the John-117 Monument, and can be viewed at the Halo 3 website.
- Museum - A live-action TV commercial featuring Retired Major Pawel Czernek, a UNSC veteran that fought in the Battle of New Mombasa alongside SPARTAN-117, reminiscing of his memories of the inspiring hero.
- Hunted - A live-action TV commercial.
- Enemy Weapon - A live-action TV commercial.
- Gravesite - A live-action TV commercial that explores the battleground and talks of Spartan 117's "death".
- Believe: The John 117 Monument - A live-action online video, describing the in-universe construction of the memorial diorama.
- On Xbox.com, there was a collection of photographs from war photographer Jake Courage titled "Shooting a Hero".
- The creators of the campaign were not informed of the story of Halo 3, leading to multiple inconsistencies with the narrative depicted in Believe and the game's story. The diorama presents a very loose representation of the Battle of New Mombasa, the most prominent contradiction with the actual events being the Master Chief's capture by a Brute Chieftain and his supposed self-sacrifice by detonating a plasma grenade. Because of these discrepancies, the Believe campaign can be understood as a cover-up operation performed by ONI Section Two to cover up the truth about the Forerunners, the Halo Array, and the Flood from the general public whilst providing a fictionalized explanation for the Master Chief's disappearance.
- Stan Winston Studio was responsible for the diorama featured in the Halo 3 Believe ads.
- The melody that was used in the Believe commercials was created by Polish pianist Frédéric Chopin and is called "Preludes #15, Raindrop".
- In the Halo 3: ODST campaign levels Mombasa Streets and Tayari Plaza, there are several graffiti where the player can read BELIEVE, a reference to the Halo 3 marketing campaign.
- A new trailer released for the game Serious Sam HD entitled "Seriously Believe" is an obvious tribute or parody to the Believe campaign, utilizing a selection of frozen in-game views in place of the models, a similar track, and a black screen at the end with the words "Seriously Believe" appearing, very similar to the original "Believe" trailer.