Where Did the Term “Dark Horse” Come From and What Does the Phrase Mean?

Sam Flynn, a traveling Tennessee horse trader, often found a horse race planned in the same town as an auction.

So he mixed a coal black racing stallion named Dusky Pete in with his workhorses, then quietly entered him in the local races and wagered heavily on Dusky Pete, who would invariably win.

As word spread of Sam’s deception, so did the cautionary expression: “Beware the dark horse.”

An unknown contestant is often called a “dark horse”.