| Honorific Prefix: | Sister |
| Birth Date: | 7 October 1929 |
| Birth Place: | Evansville, Indiana |
| Death Place: | Milwaukee, Wisconsin |
| Party: | Socialist Party USA |
| Education: |
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| Alma Mater: |
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| Occupation: | Professor |
Diane Joyce Drufenbrock (7 October 1929 - 4 November 2013),[1] also known as Sister Madeleine Sophie, was an American religious sister as a member of the Catholic School Sisters of St. Francis. She was a Christian socialist who was the vice-presidential candidate for the Socialist Party USA in the 1980 United States presidential election.[2]
Drufenbrock was born in Evansville, Indiana. In 1948, after graduating Reitz Memorial High School, she moved to Milwaukee, Wisconsin, to enter the Franciscan Sisters. A mathematics graduate of Alverno College in 1953[3] and of Marquette University,[4] she taught mathematics at Alverno College, at the University of Wisconsin–Parkside, and elsewhere around Milwaukee, including at the then-new St. Joseph High School (Kenosha) when it opened in September 1957.
Drufenbrock gained a doctorate in mathematics from the University of Illinois at Urbana in 1963. After teaching for 13 years at Alverno College, she taught at Saint Mary-of-the-Woods College in her native Indiana for 18 years.[5]
Her interest in social issues led her to join the Socialist Party USA in 1976. She ran as their vice-presidential candidate in the 1980 United States presidential election,[6] and served as that party's National Treasurer. That campaign resulted in the Party's recognition by the Federal Elections Commission as a national political party.
Drufenbrock died on November 4, 2013, in Milwaukee, Wisconsin.[1]