Film historians and critics have long regarded Brennan as one of the finest character actors in motion picture history. While the roles he was adept at playing were diverse, he is probably best remembered for his portrayals in Western movies, such as Judge Roy Bean in "The Westerner", trail hand Nadine Groot in "Red River", and Deputy Stumpy in "Rio Bravo". He was the first actor to win three Academy Awards and remains the only person to have won Best Supporting Actor three times. However, he remained somewhat embarrassed as to how he won the awards; in the early years of the Academy Awards, extras were given the right to vote. Brennan was popular with the Union of Film Extras, and since their numbers were overwhelming, he won every time he was nominated. His third win led to the disenfranchisement of the union from Oscar voting. Following this change, Brennan lost his fourth Best Supporting Actor nomination in 1941 for "Sergeant York" (the award went to Donald Crisp for "How Green Was My Valley").