There is no background for all four as a whole, however there is about them if the Chosen One takes mercenary work from Sheriff Earl Marion. Frog and his nine other gang members recently (~2241) moved into Redding, setting up shop in the abandoned Great Wanamingo Mine on the outskirts of town. Understandably, he was too dangerous to let him set up shop right near town. If the Chosen One chose to eliminate the raider threat, Earl Marion will inform the Chosen One about Frog's three brothers whom will seek revenge. When they do they and their five man gangs will be killed.
These four gangs appear only in Fallout 2.