Harriet Tubman on the $20: First African-American woman on US currency

Tubman, who led dozens of other slaves to freedom through the Underground Railroad, would be the first African-American and the second woman to appear on the front of American paper currency. Martha Washington, the wife of the first president, appeared on a $1 silver certificate in the 1880s and 1890s. In the 1860s, Native American Pocahontas appeared on the back of a $20 bill.

"Our paper bills are like pocket monuments to great figures in our history," Women On 20s Executive Director Susan Ades Stone said in May 2015. "Our work won't be done until we're holding a Harriet $20 bill in our hands in time for the centennial of women's suffrage in 2020."

Other changes to come include representations of civil rights era leaders on the $5 bill and depictions of leaders of the movement for women's voting rights on the back of the $10 bill.

Last summer, Lew announced that he was considering replacing Hamilton's image on the $10 bill with that of a woman.

Critics voiced outrage, citing Hamilton as one of the creators of the Treasury Department and the modern American financial system. Instead, they said, Jackson should be replaced on the $20 bill. The seventh president has a controversial reputation for his role in moving Native Americans off their land in the 1800s and as a slave owner.

“There are a number of options of how we can resolve this,” Lew told Politico in July. “We’re not taking Alexander Hamilton off our currency.”