Justice is a benevolent spirit of the Fade who embodies the eponymous concept of justice. Though an involuntary guest in the mortal world, his actions have made lasting repercussions on the world of Thedas.
"Justice" is not a name, it is an identity. Not all the denizens of the Fade identify with darker emotions like rage and pride. Some embody the nobler qualities found in humanity: faith, hope, compassion, valor, and justice.
Although spirits have no definite shape in the Fade, Justice takes the form of an armoured figure and chooses in place of a name, the virtue to which it aspires: Justice.
Justice finds itself housed in Kristoff's body. After recalling from Kristoff's memories that Kristoff was killed by the First and that the First's darkspawn masters who commanded the task still lives, Justice has come to the conclusion that avenging Kristoff's death would be a worthy goal.