IPA: /ˈrɪd.əl.ər/
KK: /ˈrɪd.əl.ɚ/
A person who creates or presents puzzles, especially riddles.
The riddler challenged everyone at the party with clever brain teasers.
Riddler → The word is formed from "riddle" (from Old English *rædels*, meaning a puzzle or enigma) and the suffix "-er" (meaning a person who). A riddler is a person who poses or creates riddles or puzzles.
Think of someone who creates puzzles or enigmas — that's what a riddler does, as they are a person ('-er') associated with riddles.