Given the lack of information known about The Harbinger (or Harbingers, as Charon implies there are multiple), it would likely be most helpful to compare his role to that of The Adjudicator (Asia Kate Dillon) in "John Wick: Chapter 3 — Parabellum." Both characters initially seem interchangeable, as they function as judicial agents for the High Table. Only when examining how they individually carry out their jobs is a difference made clear and The Harbinger can be better understood.
The biggest difference between the two seems to be agency. The Adjudicator, arriving at the New York Continental Hotel to investigate the extralegal execution of Santino D'Antonio (Riccardo Scamarico), has an air of confidence and authority about them. They deliver harsh judgments with a cold sneer and take liberties like determining the exact sentence a perpetrator should receive. They also employ their own assassins.
While The Harbinger also delivers judgment on the High Table's behalf, he does not appear to have any say in that judgment (hence, he is merely a harbinger of judgment rather than an adjudicator himself). It seems as though The Harbinger takes very little pleasure in doing his work, questioning the Marquis' (Bill Skarsgård) use of wanton violence and presiding over John's (Keanu Reeves) final duel with solemn bitterness. Additionally, fans probably noted that, like John, The Harbinger is missing a finger. It could reasonably be theorized that it was taken as a form of punishment — and perhaps his perpetual role of doling out cruel justice is merely an extension of that punishment.
