Vaughn had cancer and other ailments, according to Warren Christopher, the former secretary of state in the Clinton administration and O'Melveny senior partner who was Vaughn's longtime colleague.
"Bill was a mentor to a generation of adversarial lawyers," Christopher said in a statement sent to The Times.
Vaughn joined the venerable Los Angeles-based law firm in 1955 and headed its litigation department from 1986 to 1993.
He handled complex cases, including a massive antitrust case against IBM lodged by three West Coast computer manufacturers in the mid-1970s. O'Melveny won the cases, which tied up dozens of the firm's lawyers for two years.
Vaughn also waged a number of important 1st Amendment cases that, according to Christopher, "established important appellate precedents for the broadcasting industry."
Among them was the 1983 case involving Rather, who had been sued for $4.5 million in damages by Dr. Carl A. Galloway, an L.A. physician, who had accused the broadcast journalist of falsely linking him to insurance fraud in a 1979 "60 Minutes" segment. Galloway alleged that his signature had been forged on a phony medical claim that Rather had shown on air.
Rather testified for three days in the trial, which produced some embarrassing moments for the network when jurors were shown outtakes from the show, including some that indicated one subject's interviews had been rehearsed.
Vaughn, a handsome man with a powerful voice who Christopher said was "born for the courtroom," argued that Galloway had signed the bogus report and was suing Rather because he was upset at being caught.
"If you reward Dr. Galloway with even one dollar," Vaughn said in his summation, "you will signify your willingness to restrain a free press for the sake of one who entered that grimy world and was found out."
The jury sided with CBS, and its verdict was upheld on appeal.
Vaughn was born in Los Angeles on Aug. 29, 1930. He earned a bachelor's degree from Stanford in 1952 and studied law at UCLA, where he was associate editor of the law review.
He earned his law degree in 1955 and joined the O'Melveny firm the same year. After serving in the Army from 1956 to 1957, he returned to the firm and became a partner in 1964. He retired in 2002.
He is survived by his wife, Claire; sons Gregory, Tony and Jimmy; daughters Liz and Christy; a brother, Dennis; and nine grandchildren.