Short answers, pulled from the story.
A United States Note, also called a Legal Tender Note or greenback, was a type of paper money issued by the U.S. Treasury from 1862 to 1971, a span of 109 years. It was the longest-circulating form of U.S. paper money other than the Federal Reserve Note.
United States Notes inherited the nickname "greenbacks" from the earlier Demand Notes they replaced in 1862. The term distinguished them from gold-backed currency and became widely used during and after the Civil War.
President Abraham Lincoln signed the First Legal Tender Act on the 25th of February 1862, authorizing United States Notes. The notes were created to finance Union expenses during the American Civil War after borrowing and existing currency proved insufficient.
The Supreme Court initially found them partially unconstitutional in the 1870 case Hepburn v. Griswold, in a 5-3 decision written by Chief Justice Salmon P. Chase. Two new Republican appointees joined the Court and reversed that decision 5-4 in the 1871 cases Knox v. Lee and Parker v. Davis. In 1884, Juilliard v. Greenman extended broad authority to issue legal tender paper.
Distribution of United States Notes into public circulation officially ended on the 21st of January 1971. The Treasury announced in 1996 that the remaining unissued stock had been destroyed.
United States Notes were issued directly by the Treasury as a bill of credit, free of interest and without borrowing. Federal Reserve Notes are issued by the twelve Federal Reserve Banks under the Federal Reserve Act of 1913. Visually, United States Notes carry red Treasury seals and serial numbers, while Federal Reserve Notes use green.