The BFG first appeared in
first person shooters in
Doom as the
BFG9000. But in the
Doom Bible it is said the BFG was originally going to be named the
BFG 2704. This weapon actually appeared in one of the
beta versions of Doom but it behaved a lot differently to the BFG 9000: rather than
launching a single green
plasma ball it launched a large number of smaller green and orange
balls which created a large deadly
cloud and greatly
obscured your
field of view.
The BFG was changed before the final release to the familiar green ball. However, this may help to explain some of the odd behaviour of the BFG9000 (see that node for details). The reasoning behind the change is somewhat unclear. The most likely explanation was that computers at the time were unable to cope with the large number of sprites produced. However, John Romero has also claimed, "in fact, we ditched the original green&red bfg balls because they looked like Christmas".
There is a Doom Source Port named MBF which emulates some of the behaviour of the beta versions of Doom and allows you to play using the BFG 2704.