Jan is one of the main characters from the Consecution Books series.
Jan shows up somewhere probably in book 2. Not much is known about him other than that he is perhaps about 8 years older than Rebecca and posses a super-human state of laid-back-ness. We know he was rescued and mostly raised by Hunter; Rebecca remembers playing with him when she was a kid on the Saratoga. The general theory is that Jan was an orphan rescued from the Vampire galaxy. He has no last name to mention, and hits mercilessly on anything female with a pulse.