From Halopedia, the Halo wiki
Become is a marketing campaign for Halo Infinite. It features the word "Become" as a tagline, signifying that players are assuming the role of the Master Chief and becoming a hero in the Halo Infinite campaign.
The Become campaign was created by 215 McCann, the San Francisco-based advertising agency that previously created the Believe campaign for Halo 3 and the Hunt the Truth campaign for Halo 5: Guardians. Brad Meyers, the creative director at 215 McCann, viewed the Become campaign as a spiritual successor to Believe. Furthermore, Meyers directly cited the soldier testimonials from Believe as direct inspiration for the UNSC Archives series. However, the creative team shifted the focus away from John-117 being the central figure and hero to believe in, because they have observed that an increased interest in anti-heroes in popular culture. Instead, they sought out to focus on acts of heroism behind the Mjolnir armor, and tell viewers that they can be the hero they wish to be in the real world.