Jewish tradition holds that Elijah was a Gadite according to Genesis Rabba 71, and in I Kings 17:1 we read:
“And Elijah the Tishbite, who was of the inhabitants of Gilead…”
Elijah, the most famous of all the Biblical Prophets inhabited Gilead, but was not called a “Gileadite” and so it is held that Elijah was from the tribe of Gad.
There was also someone known as Gad the Seer who has a book after his namesake (I Chron. 29:29, I Sam. 22:5, II Sam. 24-11-19, I Chron. 21:9-19, II Chron. 29:25) who also is believed to be a Gadite.
Now the acts of David the king, first and last, behold, they are written in the book of Samuel the seer, and in the book of Nathan the prophet, and in the book of Gad the seer… And the prophet Gad said unto David, Abide not in the hold; depart, and get thee into the land of Judah. Then David departed, and came into the forest of Hareth… or when David was up in the morning, the word of the Lord came unto the prophet Gad, David's seer, saying, Go and say unto David, Thus saith the Lord, I offer thee three things; choose thee one of them, that I may do it unto thee. So Gad came to David, and told him, and said unto him, Shall seven years of famine come unto thee in thy land? or wilt thou flee three months before thine enemies, while they pursue thee? or that there be three days' pestilence in thy land? now advise, and see what answer I shall return to him that sent me. And David said unto Gad, I am in a great strait: let us fall now into the hand of the Lord; for his mercies are great: and let me not fall into the hand of man. So the Lord sent a pestilence upon Israel from the morning even to the time appointed: and there died of the people from Dan even to Beersheba seventy thousand men. And when the angel stretched out his hand upon Jerusalem to destroy it, the Lord repented him of the evil, and said to the angel that destroyed the people, It is enough: stay now thine hand. And the angel of the Lord was by the threshingplace of Araunah the Jebusite. And David spake unto the Lord when he saw the angel that smote the people, and said, Lo, I have sinned, and I have done wickedly: but these sheep, what have they done? let thine hand, I pray thee, be against me, and against my father's house. And Gad came that day to David, and said unto him, Go up, rear an altar unto the Lord in the threshingfloor of Araunah the Jebusite. And David, according to the saying of Gad, went up as the Lord commanded… And the Lord spake unto Gad, David's seer, saying, Go and tell David, saying, Thus saith the Lord, I offer thee three things: choose thee one of them, that I may do it unto thee. So Gad came to David, and said unto him, Thus saith the Lord, Choose thee Either three years' famine; or three months to be destroyed before thy foes, while that the sword of thine enemies overtaketh thee; or else three days the sword of the Lord, even the pestilence, in the land, and the angel of the Lord destroying throughout all the coasts of Israel. Now therefore advise thyself what word I shall bring again to him that sent me. And David said unto Gad, I am in a great strait: let me fall now into the hand of the Lord; for very great are his mercies: but let me not fall into the hand of man. So the Lord sent pestilence upon Israel: and there fell of Israel seventy thousand men. And God sent an angel unto Jerusalem to destroy it: and as he was destroying, the Lord beheld, and he repented him of the evil, and said to the angel that destroyed, It is enough, stay now thine hand. And the angel of the Lord stood by the threshingfloor of Ornan the Jebusite. And David lifted up his eyes, and saw the angel of the Lord stand between the earth and the heaven, having a drawn sword in his hand stretched out over Jerusalem. Then David and the elders of Israel, who were clothed in sackcloth, fell upon their faces. And David said unto God, Is it not I that commanded the people to be numbered? even I it is that have sinned and done evil indeed; but as for these sheep, what have they done? let thine hand, I pray thee, O Lord my God, be on me, and on my father's house; but not on thy people, that they should be plagued. Then the angel of the Lord commanded Gad to say to David, that David should go up, and set up an altar unto the Lord in the threshingfloor of Ornan the Jebusite. And David went up at the saying of Gad, which he spake in the name of the Lord… And he set the Levites in the house of the Lord with cymbals, with psalteries, and with harps, according to the commandment of David, and of Gad the king's seer, and Nathan the prophet: for so was the commandment of the Lord by his prophets.