Not much is known of Brook's past before he joined the Rumbar Pirates. What is known is that Brook was born 90 years ago and was attending some form of education in his former years, he would soon go on to become the leader of a battle convoy in a "certain kingdom", where he learned his fencing and many of his attacks received their names. These nicknames of his fencing style were given to him
Maybe he is used to be knight of same family Gunko is part of