This is called "ateji" (当て字) and is basically a form of rebus used with kanji. The practice started from the view that it was necessary to have kanji equivalents of foreign loadwords (
http://en.wikipedia.org/wiki/Japanese_w ... ese_origin)
I guess its used for the same reason you would say "effervescent" instead of "fizzy", a bunch of 80-stroke kanji that haven't been used since the US was a British colony is more impressive than plain old katakana. It's also fun to apply to your name and sign your Japanese 9 homework with it.
P.S. Suprising that no one mentioned
Salamander.
P.P.S. For the record,
Gryzor was the name of the Speccy/C64 ports of the game by Ocean.