Lillian Rose Vorhaus Kruskal Oppenheimer (October 24, 1898 in New York City – July 24, 1992) was an American origami pioneer. She popularized origami in the West starting in the 1950s, and is credited with popularizing the Japanese term origami in English-speaking circles, which gradually supplanted the literal translation paper folding that had been used earlier. In the 1960s she co-wrote several popular books on origami with Shari Lewis.
Lillian Oppenheimer ran an informal group of dedicated folders in the New York City area, and in 1978 she co-founded, with Alice Gray and Michael Shall, the non-profit Friends of the Origami Center. After Oppenheimer's death, it was renamed OrigamiUSA. As of 2016 it is the largest origami organization in the United States.
Oppenheimer was born to a Jewish family of Austrian, Hungarian, and Czech origin, the daughter of Bernard Vorhaus, an attorney who made a living importing furs. Oppenheimer is the mother of William, Molly, Rosaly, Martin, and Joseph. The three sons were all prominent mathematicians.