He may be found during the mission Kidnap Legacy Representative from Magus Mu'Drakhan, during the Story Arc A Traitorous History, in City of Villains, between levels 35 and 40.
He must be kidnapped and taken to the mission exit. As usual, you will be ambushed by Longbow troops all the way back to the mission door.
Legacy Representative had the Hit Points of a Boss of the same level as the mission owner and no attacks at all. He has a faction of Hapless Citizen.
This hapless citizen is in over his head.
Just before you capture him, he will be talking with his Longbow bodyguards:
Legacy Representative: We'll be most excited to receive the full history.
Legacy Representative: And the honored guest bringing them!
Legacy Representative: I know of this Villain! Be careful!
Longbow Officer: Don't worry, Doc. We handle punks like this every day.
After being captured:
Legacy Representative: You monster!
If left behind:
Legacy Representative: At last, Villain is distracted. Time to escape!
Legacy Representative: Curses! Captured again!
Finally, at the mission exit:
Legacy Representative You'll get your come uppance one day, Villain!