Mongo is a member of the elite military team assembled by former NEST operative Robert Epps during the Decepticon invasion of Chicago, as depicted in the film Transformers: Dark of the Moon. His name is not spoken in the film's dialogue but is confirmed in the end credits. As a former member of the NEST task force, which was a joint human-Autobot military unit, he shares a past history of fighting alongside the Autobots against the Decepticons.

In terms of personality and role within the story, Mongo presents himself as a pragmatic and prepared soldier. When Epps calls upon his former comrades to assist in a desperate, unofficial mission into Decepticon-occupied Chicago, Mongo is among those who answer the call without hesitation, demonstrating loyalty to his former commander and a willingness to face extreme danger. Upon arriving at the city's outskirts and witnessing the immense scale of destruction, the team pauses to consider the gravity of the situation, but Mongo proceeds with the mission. He is notably practical, taking stock of the team's resources in a critical moment; while handling their heavy weapons, he is explicitly shown counting their ammunition and announcing that the rocket launcher has only a single rocket, ensuring the team is aware of their limited capabilities. He participates directly in the urban combat operations, from providing cover fire for civilians to navigating the ruins of a skyscraper attacked by the massive Decepticon known as the Driller.

His primary relationship is with Robert Epps, whose call to action he answers as a trusted teammate and friend. He also works closely with the other members of Epps's ad-hoc squad, including a soldier named Stone, with whom he is seen preparing weapons. Throughout the mission, his actions are focused on supporting the group's objective, which is to assist the Autobots and the human civilians, Sam Witwicky and Carly Spencer, in stopping the Decepticon plan to enslave humanity. While his individual background is not elaborated upon, his military experience and past involvement with NEST establish him as a highly trained specialist capable of engaging with alien machines. His abilities are those of a conventional human soldier, notably including proficiency with heavy weaponry such as rocket launchers.

Mongo survives the perilous mission, which requires his team to escape a collapsing skyscraper and later engage the Decepticon Shockwave in the streets of Chicago. He does not undergo a significant personal transformation in the story, but his successful participation in the mission confirms his continued effectiveness as a soldier long after his formal service with NEST had ended.