Jackknife is one of my favorite tricks. It's a great balance of kick technique and difficulty. I see a lot of trickers now a days using this to demonstrate that they can kick trick in addition to their acrobatic power moves in their trick vocabulary.
Tricking History (from my experience):One of the first martial artists I saw execute a jackknife was one of my old coaches, David Douglas. He call it a 540 hook kick. Back in the mid 90's there weren't forums or message boards so tricks would come out slowly to the public. You had to be in the sport karate tournament scene to stay up to date with the lingo. In 2000 through message boards like Bilang.com trickers started calling it a Jackknife.
Circa 1997 - As you can see David was very pro hook kick.
One of the main reasons why I focused years on training and analyzing them.