Computer scientist Mary Ann Horton is playfully modest about one of her best-known achievements. She calls uuencode—short for Unix-to-Unix-encoding—a “dumb little program” that she wrote in 1980, even though it has since gained wide recognition as the “forerunner to e-mail attachments. Sure, it’s nice,” she says, when asked how it feels to have catalyzed a system that millions now use every day. “I don’t think the e-mail attachment is that big a deal.” Perhaps that’s because, in addition to Horton’s many other technical accomplishments, she is also a pioneering transgender activist. In the 1990s and 2000s, Horton played a key role in encouraging American companies to add the categories of gender identity and gender expression to their non-discrimination policies—and to provide transgender health benefits.