User blog comment:TheBody84/Ichigos father being the former Kenpachi/@comment-1591878-20090924065850

he is ex royal guard. "zero squad" that captains are promoted to. they elude to it in episode 206. my guess is that he l was 3rd squad captain and left the soul society with ichigo's mom. she was either another captain of related to the spirit king. that would explain why ichigo was referred to as a pure blood in episode 111 by grand fisher.