When someone asked John “Who he was” that for them wasn’t really a question of his background. They knew who he was in terms of his parents and family background.They were really asking another question. They wanted to know if John was an important person in the plan of God to bring about the redemption of Israel. John however refuses to say that he was a fulfilment of Old Testament prophecy. Instead he describes himself as a “voice”.
2 Timothy 3: 16-17
All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the servant of God may be thoroughly equipped for every good work.