According to the book of Genesis, Gad is a son of Jacob and Zilpah, being the first son of Zilpah by Jacob, and the seventh of Jacob overall. His name means "luck" or "fortunate" in Hebrew, the root verb meaning "cut" and "divide", as in "divided out". Gad is the eponymous founder of the Tribe of Gad. According to critical scholarship, Gad is merely a non-historic eponym for the tribe (i.e. derived from the tribe, rather than vice-versa). Wikipedia
The definitive Wikipedia entry for Gad. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Gad_%28Biblical_figure%29