Step 1 : Introduction to the question "Who is the only First Lady to ever be featured on U.S. paper currency?"
...Martha Washington is the only First Lady ever to appear on U.S. paper currency. Her portrait was first featured on the $1 Silver Certificate in 1886 and 1891, making her the first—and so far, only—woman to be depicted on a federally issued banknote. In 1896, she was again featured on the $1 Silver Certificate, this time alongside her husband, George Washington, on the back of the note. These Silver Certificates, which were backed by the government’s silver reserves, were gradually phased out over time, with the last series issued in 1957.