A person or thing that causes affliction, suffering, or distress to others.
From afflict plus the agent suffix -er, which creates nouns for someone who performs an action. Relatively rare, as the concept usually doesn't need a specific agent noun.
English lets you make agent nouns freely with -er (teach→teacher, afflict→afflicter), but some stick in the language while others sound awkward—we say 'teacher' constantly but 'afflicter' almost never.
Complete word intelligence in one call. Free tier — 50 lookups/day.