Gustav Bird, the taller and thinner of the Bird Brothers, was an antique collecter. Gustav Bird is portrayed as wearing a blue coat, red tie and white shirt, and bears a glum-looking countenance. He and his brother, Max, had obtained one of the three ship models of the Unicorn. The pair owned Marlinspike Hall before it was claimed by Captain Haddock.
In The Secret of the Unicorn, the brothers kidnap Tintin in the belief that he has one of the scrolls, and lock him in the basement of Marlinspike Hall. Tintin escapes, and the Bird Brothers are arrested. Gustav then admits that the three scrolls, when put together, give the location of the treasure. Both him and his brother are mentioned in the Castafiore Emrald and have a slight appearance in Tintin and Alph-Art.