Extremely insane large-displacement two-stroke motorcycle made by Kawasaki. 'Demands an experienced rider', said the sales brochure. Yes, it demanded one. And then it generally killed them.
It was fast. It was very, very fast. But the frame was too weak, neither rigid enough nor capable of absorbing the stress imparted by the engine, and tended to break. Even if it didn't break while you were riding it, the handling was appalling and tended to insert the bike into a hedge very easily.
The H1 was a 500cc two-stroke twin. Its successor, the H2 was a 750cc two-stroke triple; it compounded the problems of the H1 by being even more powerful and the middle cylinder didn't get cooled enough and tended to seize, leading to even more death and destruction.
The thing about two-strokes is that the tuned exhaust as invented by Walter Kaaden of MZ gives them an extremely narrow power band. This makes them feel all sluggish until suddenly they go completely mental. Wonderful, if that's what you're into. In the case of the H1 and H2, though, the bike was just too powerful for that sort of behaviour. Most H1s crashed. Those that didn't crash blew up and crashed.
Kawasaki never really got the hang of two-strokes. That was okay though because while all this was going on they were developing the Z1, which was a real world-changer.