Refers to a person who fishes, often with a nuance of skill or dedication.
He becomes an angler on weekends.
Internet troll
Internet slang; refers to someone who posts inflammatory or off-topic messages to provoke others.
That forum has many trolls.
Standard spelling with okurigana.
Variant without okurigana; less common but still used.
Compound of 釣り (fishing) and 師 (master, specialist). The Internet slang sense is a metaphorical extension, likening a troll to someone who 'fishes' for reactions.