IPA: /ˈθæŋkər/
KK: /θæŋkər/
A person who expresses gratitude or appreciation.
She is a thanker who always shows her appreciation for others' help.
Thanker → The word is formed from "thank" (from Old English "þanc", meaning gratitude or thanks) and "-er" (meaning a person who). A thanker is a person who expresses gratitude.
Think of someone who expresses 'gratitude' ('thank') — the '-er' just means a person. A thanker is someone who shows thanks.