Cosmonaut Dimitri is a minor human character appearing in the film Transformers: Dark of the Moon. He is portrayed as an ex-cosmonaut from Russia whose lunar mission was abruptly cancelled. Following the shutdown of their expedition to the Moon in 1972, Dimitri and a fellow cosmonaut named Yuri went into hiding, eventually settling in the United States.

In terms of personality, Dimitri is depicted as a gruff and reluctant individual. He is characterized by a low tolerance for what he considers intrusive or unusual questioning. Specifically, he does not like to be bothered by what he calls "weirdos," particularly those who inquire about the cancellation of his mission to the Moon. This suggests a man who may be weary of his past and is not eager to revisit the mysterious circumstances that ended his career as an astronaut.

Dimitri's primary role in the story occurs when he and Yuri are tracked down years later by the former paranormal investigator Seymour Simmons and the protagonist Sam Witwicky. Simmons and Sam are seeking answers about the true nature of the space race and the secrets hidden on the Moon. Dimitri reluctantly provides the crucial information they are seeking, explaining that the Russian mission took photographs of the dark side of the Moon. These images revealed strange rock formations that did not appear natural, specifically looking as though they had been deliberately dragged into place. This revelation confirms that extraterrestrial activity had been discovered decades earlier, directly implicating the Transformer known as Sentinel Prime and the technology known as the Pillars. When Sam and Simmons become excited and begin discussing the Autobots and related topics, Dimitri’s grumpy and dismissive demeanor remains evident, as he clearly finds their enthusiasm bothersome.

His key relationship within the narrative is with his companion Yuri, as they are the only two surviving witnesses from their original mission. Together, they represent the hidden human history of the Transformers' arrival on Earth. The character has a brief exchange with Simmons's assistant, Dutch. When Dutch attempts to speak Russian, Dimitri flatly responds, "We do speak English," demonstrating his no-nonsense attitude and further highlighting his irritation with the situation. As a minor character, Dimitri does not undergo significant development; his function is to serve as a plot device that delivers a vital piece of the backstory to the main characters. His most notable ability is simply his firsthand knowledge of the lunar anomaly, making him a key witness to the cover-up that drives the film's central conflict.