Leon has long blue (dyed) hair, which he keeps in a ponytail. His eyes match his hair and he wears glasses. He also has sharply pointed canines that he enjoys flashing at people at every opportunity. He was sliced open with a katana during the 2008 Mary Sue Invasion, and likely still bears the scar.
Leon tries his best to be cool-headed and aloof but usually fails, growing immersed in his various cases despite himself. He enjoys keeping people guessing and can be slightly mischievous at times. For instance, he finds it highly amusing to listen to the speculation about his origins (due to his odd appearance). He occasionally claims to dislike his job on the grounds of being overworked but his complaints tend to just attract ridicule.
Details of Leon's recruitment are fairly sketchy and tend to be conjectural. This is because he refuses to tell anybody either his home continuum or in fact his species. This means that very few people about the PPC know that he is in fact A) completely human and B) from the Real World.