Anti-slavery crusader Harriet Tubman will become the first African-American on the face of US paper currency, and the first woman in more than a century, when she replaces former president Andrew Jackson on the $20 note.The US Treasury said on Wednesday that Tubman, who was born into slavery in the early 1820s and went on to help hundreds of slaves escape, would take the centre spot on the front of the note, whereas Jackson, a slave owner, would be moved to the back.Introduced alongside a slew of other changes to the $5 and $10 notes, the redesign gives the Treasury "a chance to open the aperture to reflect more of America's history," Treasury Secretary Jack Lew said.A new $10 bill will add images of five female leaders of the women's suffrage movement, including Sojourner Truth and Elizabeth Cady Stanton, to the back, while keeping founding father Alexander Hamilton on the front. The reverse of a new $5 note will show former first lady Eleanor Roosevelt and civil rights leader Martin Luther King jnr, officials said. Former President Abraham Lincoln will remain on the front.Lew said the designs should be unveiled by 2020 and go into circulation "as quickly as possible", although he declined to say when. He said the $10 bill was scheduled to go out first.The long-awaited decision to replace the seventh president of the US with Tubman followed months of outreach by the Treasury regarding which woman should be featured on a bill.The debate began when the Treasury announced plans in June to feature a woman on the $10 note, prompted partly by a young girl's letter to President Barack Obama that criticised the lack of women on US currency and a social media campaign last year called "Women on 20s."Jackson, a hero of the War of 1812's Battle of New Orleans, was president from 1829-1837. But he has been criticised for his treatment of Native Americans and for owning slaves.After considering hundreds of candidates, Lew said, Tubman was chosen for her leadership and work helping others."It's the essential story of American democracy, about how one person, who grew up in slavery, never had the benefit of learning how to read or write, could change the course of history," he said.Tubman grew up working on a Maryland plantation and escaped in her late 20s. She returned to the South to help hundreds of black slaves to freedom and worked as a Union spy during the Civil War. She died in 1913.Women have not been depicted on US bills since Martha Washington, who was on the $1 silver certificate from 1891 to 1896, and Pocahontas, who was in a group picture on the $20 bill from 1865 to 1869.On coins, Sacagawea, a Native American who assisted the Lewis and Clark Expedition, is featured on the gold dollar, and suffragist Susan Anthony is on the silver dollar. Deaf-blind author and activist Helen Keller is on the back of the Alabama quarter.Tubman became the top-trending hashtag on Twitter shortly after the news broke, with more than 100000 tweets and mentions online.Democratic presidential candidate Hillary Clinton, who is campaigning to become the first female US president, praised Tubman as "a woman, a leader, and a freedom fighter" on Twitter and said she could not think of a better choice. ..