The Elephant trap was first recognized in Brazil, 1848. Between Karl Mayet vs Daniel Harwitz.
The trick got caught on and was known as "The oldest trick in the game." Later on, it became known as the elephant trap. In Russian, Bishop translates to Elephant, hence the name.
Why the bishop?
The elephant trap uses the bishop to trap the queen. This trap is a spin off of the Qeens Gambit declined. When one tries to take someone queen, they respond wth this trap and end up trading queens.
This trap works best when white opens and black starts the trap. It leaves both players without a queen, white down both a bishop and a knight.