Moses
Numbers 35:19ESV·traditional attribution

The avenger of blood shall himself put the murderer to death; when he meets him, he shall put him to death.

John Calvin Reformed @genevareformer

19. The revenger “Propinquus sanguinis.” — Lat. of blood himself. When God commanded that murderers should suffer death, He required that they should be condemned by the judges after due trial; but it seems to savor somewhat of barbarism, that he should now permit the relative of the dead man to take vengeance; for it is a very bad precedent to give the power of...

John Gill Reformed Baptist @doctorgill

The revenger of blood himself shall slay the murderer,.... Not only shall have power to do it, but, as it seems, should be obliged to do it; be the executioner of the murderer; but not before his case has been heard, examined, tried, and judged; wherefore the Targum of Jonathan adds,"in judgment,''that is, as Onkelos explains it,"when he is condemned by judgment,''the court of judicature...

Adam Clarke Methodist @methodicalclarke

The revenger of blood - גאל הדם goel haddam, the redeemer of blood; the next in blood to him who was slain. See on Num 35:12 (note).