Hop Gar is one of the branches that developed from the Tibetan martial art originally known as Lion's Roar. According to legends, it was developed by a Tibetan Lama. It was brought into Southern China where it became known as Lama Pai, or simply The Style of the Lamas. One branch of it became known as Hop Gar, or the Syle of the Hero, as it was named after it's prominent practitioner who supposedly was a local fighter for the oppressed (I can't remember his name). In the 1950s, Hop Gar branched again and became known as Bak Hok, or White Crane, but is the Tibetan White Crane to distinguish it from Fukien White Crane (ENTIRELY different system). According to legend, the original Lion's Roar was developed when the meditating Lama witnessed a fight between a "mountain ape" and a crane. Currently, I believe all three branches exist, Lama Pai, Bak Hok, and Hop Gar. There are some differences, but essentially they are the same system.
It is a very long-range system, using a unique type of body torque to deliver extremely powerful hand-strikes, kind of like swinging a baseball bat, only it is your fist. It has to be done with a tremendous amount of speed, since the long-range punches can leave you somewhat exposed. The forms tend to be lengthy and very difficult since they move A LOT and take a lot of space, and you have to move FAST. I practice the Tibetan White Crane, and enjoy it quite a bit. It is probably also somewhat of a lesser-known art than others, with fewer qualified instructors.
Hope this helps, let me know if you would like more info.
Michael