Technically, John the Baptist was not a disciple in that he did not follow Jesus in his ministry. However, he was a believer in Jesus, calling him "the lamb of God who takes away the sin of the world."
John 1:29 The next day he saw Jesus coming toward him, and said, "Behold, the Lamb of God, who takes away the sin of the world!
John 1:36 and he looked at Jesus as he walked, and said, "Behold, the Lamb of God!"
I hope you have found this helpful.