Lucille Douglas Cochrane (February 19, 1920 in Boston, Massachusetts - November 8, 2003 in Old Westbury, Long Island, New York) was an American stage actress, author, columnist, horsewoman, fashion designer, and socialite who achieved a degree of fame as a fashion icon. She was frequently seen wearing elegant designs by famous designers like Mainbocher. Her unfussy, clean-cut style was seen as typically American.

Her father, Alexander Lynde Cochrane, was an investment banker. She acquired C.Z. from her younger brother. She dabbled in acting, including an appearance in the Ziegfeld Follies in 1944.

On March 8, 1947, she married Winston Frederick Churchill Guest (1906-1982), a national polo champion, member of the Guest family, grandson of Henry Phipps, a great-grandson of the seventh Duke of Marlborough, and Winston Churchill's second cousin. Ernest Hemingway was best man at the wedding, which took place at Hemingway's home in Havana, Cuba. The couple had two children, Alexander and Cornelia; Cornelia was named the 1980s "Deb of the Decade". C. Z Guest was pictured on the cover of the July 20, 1962 issue of TIME magazine as part of an article on American society.

After a horse riding accident in 1976, Guest was asked by the New York Post to write a column on gardening. Her first book, First Garden, was illustrated by her friend Cecil Beaton. Other friends included Truman Capote, Barbara Hutton, Gloria Guinness and Loel Guinness and the Duke and Duchess of Windsor who were the godparents of their children.

Much photgraphed, she was also painted by Diego Rivera, Salvador Dali, and Andy Warhol.

In 1985, Ms. Guest designed a small fashion collection consisting mainly of cashmere sweaters that was introduced at a show of the designer Adolfo. In 1986, she expanded her design work to include a limited line of sportswear sold under license, and in 1990 she came out with a fragrant insect repellent and other garden merchandise.

C. Z. died aged 83 as a friend was driving her to the hospital due to her experiencing breathing difficulties while at home.