The appearance of presidents on multiple U.S. currencies is a result of historical decisions, commemorative acts, and a general tradition of honoring significant figures. While there isn't one overarching rule, several factors have contributed to this phenomenon:
Historical Significance: Presidents who played pivotal roles in shaping the nation are often chosen. For example, George Washington, the first president, is a natural choice for prominent currency, appearing on the dollar bill and the quarter. Abraham Lincoln, who led the country through the Civil War and pushed for the abolition of slavery, is featured on the penny and the five-dollar bill. Thomas Jefferson, the primary author of the Declaration of Independence, is on the nickel and the two-dollar bill.
Commemoration: Many presidential currency appearances have been specifically to commemorate important anniversaries or events. The Lincoln penny, for instance, was released in 1909 to mark the 100th anniversary of his birth. The Washington quarter debuted in 1932 for the 200th anniversary of his birth. John F. Kennedy was placed on the half-dollar coin in 1964 shortly after his assassination as a national remembrance. Franklin D. Roosevelt was added to the dime in 1946, the year after his death, in part to honor his role in establishing the March of Dimes.
Tradition and Popularity: While early U.S. coins often featured allegorical figures like Lady Liberty, public sentiment shifted to favor portraits of leaders. Over time, certain presidents became strongly associated with particular denominations.
Secretary of the Treasury's Discretion: The Secretary of the Treasury ultimately approves the designs and individuals featured on U.S. currency. There's no specific law dictating which president goes on which denomination, beyond the rule that the person must be deceased.
It's also worth noting that non-presidents like Alexander Hamilton and Benjamin Franklin are featured on currency, recognizing their significant contributions to the nation.