The chickenpox virus was originally thought to be related to the much more dangerous smallpox virus, but in the early 1900s it was realized that it is not at all like smallpox. Chickenpox, or varicella, is a member of the herpesvirus family of virues. That means it is related to Epstein-Barr virus which causes mono, and herpesvirus which causes fever blisters and other things.

As far as I can tell (I'm looking at an introduction to the history of virology from 1978) the guys who first described the chickenpox virus were E. Paschen, 1919; EE Tyzzer, 1906; von Bokay 1909. In 1954 Weller discovered that chickenpox and shingles are caused by the same virus (sorry this isn't more useful).

Chicken pox generally breakout in epidemic form. For instance, it is believed that 90% of susceptible people (people who haven't had chicken pox before) will get it when they are exposed to the virus. It will often run through a school or daycare or house very rapidly. The good thing about chickenpox is that it is more of an annoyance than a really serious disease.

Here are a couple websites which I found useful.
WebMD
thecountrydoctor.com
Louisiana State University
Center for Disease Control

Good luck!
-Sarah