Robert Stack, who made a career out of playing (and sometimes spoofing, as in ''Airplane!'') ramrod-stiff authority figures, died Wednesday afternoon of heart failure at his Hollywood home, the Associated Press reports. Best known for the TV series ''The Untouchables'' and ''Unsolved Mysteries,'' the 84-year-old actor had been treated for prostate cancer last fall but had otherwise been in good health, his wife, Rosemarie, told AP.
Stack, whose Hollywood career began in 1939, won an Emmy playing mob-pursuing G-man Eliot Ness in ''The Untouchables,'' which ran from 1959 to 1963 and inspired the 1987 Brian De Palma movie of the same name. The sense of authority that emanated from his square jaw and rumbling baritone served him well in such films as ''The High and the Mighty'' and ''Written on the Wind'' (for which he earned an Oscar nomination in 1958), and as the host of TV's ''Unsolved Mysteries.''
He played similar roles, but with tongue in cheek, in such comedies as ''Beavis and Butt-Head Do America,'' ''Baseketball,'' and the laugh classic ''Airplane!'' Despite his sober onscreen demeanor, he didn't take himself or Hollywood too seriously; as he told AP in 1998, ''It's all malarkey; even the wonderful part is malarkey.''