The Black Knight Satellite was discovered in 1959 (some accounts are 1960, though it seems the images of it were taken in 1960). The Black Knight was an object noticed in the higher polar latitudes by a number of observers. It was quickly linked with some odd radio transmissions that several HAM radio operators had picked up, which were later deciphered into star charts). It was dubbed the Black Knight by the press.
The official response is that the the debris was a piece of the housing from Discover VIII, one of a long series of secret test satellite launches the US Government was doing at the time. It eventually lost orbit and fell to earth. And that the HAM operators were just a little over zealous.
Several pictures were later snapped of the object and used to precisely identify the object.
I couldn't find the link on the NASA site, might warrant looking into the Blue Book.