Gad was one of the twelve sons of Jacob, making up the twelve tribes of Israel. “Gad” means Mazal Tav, “good luck” (Rashi).
And Leah said, “Luck has come”; so she named him Gad (Breishit, 30:11) .
According to another opinion (Ibn Ezra), “Gad” means a “troop” (as the Hebrew Gedud). Moshe Rabbenu, in his blessings the Tribes of Israel, compared the descendants of Gad to a lion. The tribe of Gad was known to the mighty warriors who would strike down Israel’s enemies.
He also gave a hint that the tomb of Moshe will be hidden in Gad’s portion of the Land of Israel (see Rashi on Devarim, 33:20-21).
According to tradition, Gad was born (and died) on the tenth day of this month, Cheshvan (Shemos Rabba 1: 5). He lived to be 125 years old. (Yalkut Shimoni, Shemot, remez 162)