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benefactor; patron; person to whom one owes a great deal; person to whom one is (deeply) indebted
恩人のおかげで助かりました。
Thanks to my benefactor, I was saved.
恩人に感謝の手紙を書きました。
I wrote a thank-you letter to my benefactor.
恩人のおかげで大学に入れました。
Thanks to my benefactor, I was able to enter university.