Guy Day (born circa 1933) is an American advertising executive who co-founded Chiat/Day with Jay Chiat in 1968. The agency went on to do memorable work for Apple Computer, including the Macintosh "1984" Super Bowl commercial. Day originally founded an agency called Faust/Day with Tom Faust. When Faust left, Day called Chiat to discuss a merger with Jay Chiat & Associates. Day won a coin toss to see who would be the president of the new agency. Wikipedia
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