Harry's Hogwarts rival (5)
I believe the answer is:
draco
'harry's hogwarts rival' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for draco that I've seen before include "death-dealing lawman" , "Harsh legislator" , "Constellation, the Dragon" , "Ruthless lawmaker" , "Athenian statesman" .)