Issued between 1980 and 1999, the Great Americans definitive series features 63 designs, making it the larges set of face different Regular Issue stamps issued in the 20th century. One stamp honors a couple (Lila and Dewitt Wallace) while the remaining 62 commemorate individuals. The series is characterized by a standard definitive size, simple design and monochromatic colors. The Bureau of Engraving and Printing produced most of the stamps, but some were printed by private firms. Several stamps saw multiple printings. The result is many different varieties, with tagging being the key to understanding them. The 29¢ Great Americans stamp pictures Thomas Jefferson.