Mr. Elliott took over for Ogilvy as chairman in 1975, after a steady rise that began when he joined the agency in 1960. He had been hired to win Shell Oil, which became Ogilvy's biggest account at the time, and went on to the distinguish himself as an exceptional manager of accounts and, eventually, of one of the most important ad agencies.
His greatest strengths were scouting talent and skillful handling of employees, said longtime friend and colleague Bill Phillips, chairman emeritus at Ogilvy. "He had a good sense of people and a good eye for people," Mr. Phillips said. "He had a strong point of view, but never let his high position get him off track."
Mr. Elliott was born in New York in 1921. His father was an investment counselor and his mother sold real estate. He was educated at private institutions including the Browning School, St. Paul's School in Concord, N.H., and Harvard University.
He served in the U.S. Marine Corps during World War II and then started in advertising. His first job was as a copywriter earning $60 a week at Batten, Barton, Durstine & Osborn, the agency that later became BBDO Worldwide. He moved into account management, an area he described as "less demanding" than copywriting, after concluding he was not great as a copywriter.
"I was pretty good," he once told Ogilvy employees, "but not good enough. I could execute campaigns but I never came up with the big ideas. ... I have stood in awe of people who could come up with big campaign ideas."
Others have chalked that up to Mr. Elliott's humility. "There is a fair amount of modesty in that," said Mr. Phillips. "The reality is you never know what the big ideas are. Sometimes they come from ideas you think will be small."
In a memo to her staff sent last week, Ogilvy Chairman-CEO Shelly Lazarus said "Jock ran Shell brilliantly-some very memorable advertising was made under his stewardship-and then he ran the company, allowing his partner David Ogilvy great freedom to be creative chief and to move into retirement. Much is known of David's great leadership, but Jock also put an indelible mark on our company."
In addition to his career in advertising, Mr. Elliott was an avid collector of books about Christmas and its customs. The oldest item in his collection, according to a 1999 story in The New York Times, was a leaf from a "book of Hours" from 1430, printed before the invention of movable type, that showed the Adoration of the Magi. Mr. Elliot told the reporter of his six-foot-long stocking, which his wife, Eleanor, "fills up with underwear," and his tradition of reading "The Ballad of the Harp-Weaver" every Christmas to her. "We go to sleep with a warm heart and a moist eye," he said. Four years later, his book, "Inventing Christmas," was published.
Mr. Elliott died of a cerebral hemorrhage. His survivors include his wife, Eleanor Thomas Elliott, his brother Osborn and numerous nieces and nephews.