Order of the Phoenix
OOTP is perhaps the book that gives us the most insight into Percy. Percy has a row with his parents over where their loyalties lie *with the Ministry or with Dumbledore*. Of course Percy sides with the Ministry & Aurthur and Molly support Dumbledore. What with this, Percy packs his things and moves to London, cutting off all communication with his family.
Percy aquires the job of Junior Assistant to the Minister of Magic, which only adds to his pompousness. Percy sends a letter to his youngest brother Ron, in which he congradulates Ron on becoming a Gryffindor prefect, and asks that he not be influenced by their parents decision to side with Dumbledore. He also mentions that he thinks it would be best for Ron to sever ties with Harry.
In OOTP, Aurthur Weasley is attacked by a snake with a bite that could have been fatal; Percy makes no effort to contact his dad at St.Mungo's (the hospital). Furthurmore, at Christmas he sends his Weasley sweater back with no note.
Percy's demenor is quite atrocious in this book, which I find interesting and exciting. Percy has always been one of my favorite characters, and I am glad that now we get to hear more about this complex character.
It will be very interesting to see what will happen between Percy and his family now that Fudge*the minister* can no longer deny that Voldemort is back.