The Bird Brothers (French: Les Frères L'oiseau) Max and Gustav, were antique collectors who had one of the three Unicorn models. The Bird Brothers lived in Marlinspike Hall before Captain Haddock gained ownership of it and likewise before Nestor worked for Captain Haddock, he worked for the Bird Brothers. In the book The Secret of the Unicorn, the brothers disguise themselves as delivery men so they are able to kidnap Tintin without being noticed. They keep him as a hostage in Marlinspike Hall because they believe Tintin has the scroll. Later in the comic Tintin breaks free from his prison and the Thompsons arrest them both. Upon being arrested Gustav confesses that when all three scrolls, when put together, resemble a treasure map. In Red Rackham's Treasure, it is revealed that Max Bird has escaped from prison and had been spotted near the Sirius, the ship used by Tintin and Haddock to hunt for Red Rackham's treasure. As a result Thompson and Thomson accompany the expedition in case he confronts them. Despite this, he never appears, which the detectives conclude was due to their presence. The Bird brothers were depicted in sketches for the unfinished Tintin and Alph-Art, hinting that they may well have been intended to appear in it.
In the film adaptation of the two books the brothers feature in, The Adventures of Tintin: The Secret of the Unicorn, the Bird Brothers are completely replaced as the main antagonists by a reimagined Ivan Ivanovitch Sakharine. They do make a cameo appearance in the movie, at first stealing Tintin's miniature-figurine of the Unicorn, and the second time with their portraits appearing as samples of the sketch artist that Tintin was being painted by at the start of the film, who just so happens to be Tintin's creator, Hergé.