A person who argues against something or challenges a claim; someone who disputes or refutes.
From 'controvert' + '-er' (suffix for the agent who does the action). It directly names the person who controverts or disputes claims.
A controverter is an argument's natural opponent—they're the person who, when you make a claim, immediately says 'but what about...?' making them essential in science and law.
Complete word intelligence in one call. Free tier — 50 lookups/day.