Are Hillary Clinton, Eleanor Roosevelt, and Jackie Kennedy the obvious trinity? I'll still put an 'OTHER' option if you want to support another FLOTUS being more iconic or just as iconic as these three.
HILLARY CLINTON
The most powerful of all FLOTUS's. No other First Lady served in the U.S. cabinet, was elected to the Senate, and won a major political party's nomination for the presidency in her own right. She played a pivotal role in policy making in her husband's administration, including health care, and was a huge factor in getting major bills passed through Congress.
ELEANOR ROOSEVELT
A woman before her time. She was outspoken, spoke up for women and minorities, and was the first First Lady to hold press conferences, write a syndicated column, and speak at a national convention. She was held in high regard and had almost universal respect.
JACKIE KENNEDY
The most stylish First Lady. Her pill box hats are iconic and she became a symbol of fashion for women worldwide during her husband's presidency.