There are at least two people in the Bible named Gad. One was a prophet and the other was one of the 12 sons of Jacob.
Gad, the son of Jacob, was the seventh son of Jacob. His mother was Zilpah, who was Leah's maid. He was the founder of the tribe of Gad. He made the journey with Jacob and the family from Padan Aram to Canaan, and later, to Egypt. In the census taken in the second year after the Exodus, the tribe of Gad numbered 46,650 (Numbers 2: 14-15).
At the time of the second census, there were 40,500 (Numbers 26:18). In the blessing of Jacob (Genesis 49:19) it is said, "Gad a troop shall tramp upon him, but he shall triumph at last." In the blessing of Moses (Deuteronomy 33:20), it is said, "Blessed is he who enlarges Gad.". In Revelation 7:1-8, Gad is among the tribes who are promised the Seal of God for 12,000 of its members.
The other Gad - the prophet - first appears in the Bible to persuade David to leave his place of safety in Moab and return to Judah, where the insanely jealous King Saul awaited him. later on, after David had a census taken of Israel, Gad gave David a choice of punishments from the Lord for carrying out that rash act. David chose the three day plague.
During the plague, which took 70,000 lives, Gad, the prophet, told David to build an altar to the Lord on the threshing floor of Araunah the Jebusite (2 Sam. 24:18). The burnt offerings from this altar, caused the Lord to stop the plague. The threshing floor, later, became the site of King Solomons Temple. In 2 Chronicles 29:25, Gad, along with David and the prophet Nathan, "stationed the Levite's in the Lord's house with cymbals, harps and lyres", according to the prescriptions "from the Lord through His prophets." Gad is described as David's seer in 1 Chronicles 21:9.
The name Gad means Gad "Good fortune."