A combination of factors led to his playing old men at an early age (he was only 45 when he won the Oscar for his septuagenarian horse breeder in "Kentucky"). First, he had fallen victim to a gas attack during WWI which permanently affected his vocal chords, resulting in the harsh, reedy tones that became his signature. Second, while working as a stuntman in 1932, he had lost all his teeth in an accident which allowed him to film with or sans choppers, depending on the requirements of the role.
From 1930 to 1960, Brennan was constantly in films of the highest quality, acting for the best directors of this era. For John Ford in "My Darling Clementine" (1946), he turned in an excellent performance as a crusty old horse thief and father of a gang of ne'er do wells. His Groot Nadine supplied welcome comic relief in the midst of Howard Hawks' tough melodrama "Red River" (1948) while maintaining a character as rough and ready as the next, and again for Hawks, he provided Bogart with a wonderful drunken sidekick in "To Have and Have Not" (1944). Brennan gave a typically outstanding characterization as Ezra Peavy, the squirrel-hunting aide-de-camp to Andrew Jackson, in Cecil B DeMille's swashbuckling saga of Jean Lafitte, "The Buccaneer" (1938), and tormented lawman Kirk Douglas with a song from his jail call in Raoul Walsh's "Along the Great Divide" (1951). He worked most often with Hawks (six times in all) and as Stumpy, the cantankerous cripple in their final collaboration "Rio Bravo" (1959), he turned in one of his top performances, a comic masterpiece that was a culmination of all the loyal, crabby old-timers he had played through the years. Directors knew what to expect when they hired Walter Brennan, and time after time he delivered the goods.
Television introduced him to a whole new generation of viewers. As Grandpa Amos McCoy in ABC's popular sitcom "The Real McCoys" (1957-62; CBS, 1962-63), Brennan delighted a wider audience with his porch-rockin', gol-darnin', consarnin', meddlesome ways, and the show's success paved the way for a host of rural comedies to follow (e.g., "The Andy Griffith Show", "The Beverly Hillbillies", "Petticoat Junction" and "Green Acres", to name a few). He followed "The Real McCoys" with "The Tycoon" (ABC, 1964-65), in which he played (no surprise here) a cantankerous and eccentric millionaire and finished off his small screen career as Will Sonnett in "The Guns of Will Sonnett" (ABC, 1967-69), co-starring Dack Rambo as his grandson Jeff. Although there were a few films during this period (primarily children's fare like 1967's "The Gnome-Mobile"), the golden age of the Western had passed, and Brennan, a grand old war horse, was perfectly content to graze the lush green pastures of television.