Why is Andrew Jackson on the $20 bill? The answer may be lost to history.

Sometimes, popular history has a way of turning the dead into heroes or villains. In the case of Andrew Jackson, the current narrative leans towards the latter. And yet, for nearly a century, a portrait of America's seventh president has graced the $20 bill — something one new group wants to change by replacing Jackson with a woman.

Historians have some ideas as to why putting Jackson on the $20 seemed like a good idea in 1928, when his face was selected to replace Grover Cleveland's. But as it turns out, nobody seems to know for sure why a Treasury Department committee assigned Old Hickory's portrait to the bill.

No really, we checked. The Treasury Department, which has the authority to determine who appears on what bills (so long as that individual is already dead), says on its Web site that its own historical records "do not suggest" why certain presidents ended up on certain bills during a blitz of portrait selections in 1928.