Gad is the first son of Yaakov and Zilpah, the handmaiden of Leah, and the seventh son, overall of Yaakov. According to Midrash “Yalkut Shimoni,” he was born on the tenth of Cheshvan and, according to Rashi, citing an anonymous Midrash, he was born circumcised. When Gad was born, we find, “Leah said, ‘Bo Gad’ –‘Good luck has come’ (Bereshit 30:11), so she named her son ‘Gad.’ ”
In his blessing to Gad, Yaakov says, “Gad will recruit a regiment that will return on its pathway,” (Bereshit 49:19) alluding prophetically to the historical fact that the Tribe of Gad, together with the Tribe of Reuven and half the Tribe of Menasheh, would remain on the East Side of the Yarden (the River Jordan), rather than cross the Yarden into Eretz Yisrael, because the pasture-land on that side of the Yarden seemed better-suited to their large flocks of cattle. Moshe would agree to this arrangement on condition that they would accompany the rest of the Tribes into the Holy Land, and assist them in the military conquest of the Land. Gad and the other Tribes agreed to do this, and Yaakov Avinu records the fact that Gad would not lose a man, and they would return to the East Bank, complete, after assisting the other Tribes.
In his blessings to the Tribes on the last day of his life, Moshe Rabbeinu praises the Tribe of Gad for expanding the boundary of Eretz Yisrael eastward (Devarim 33:20), for being great and fearless warriors (ibid.), for having the additional reason for remaining on the East Side of the Yarden; namely, that they wanted to be where the “mechokek,” the great law-giver, Moshe himself, would be buried (ibid., 21). He also praises them prophetically for keeping their promise and marching at the forefront of the Tribes of Israel, during their conquest of the Land of Canaan, which would become “Eretz Yisrael,” before returning eastward. (ibid.)
Gad, the great founder of the Tribe called by his name, was buried on the east side of the Yarden, in Romia, which was part of the portion of land allocated to his Tribe (“Sefer HaYashar,” end of Sefer Yehoshua).