noun
A person who acts based on self-interest, often at the expense of others. Can be used in both critical and descriptive contexts.
彼は自分のことしか考えない利己主義者だ。
He is an egoist who only thinks about himself.
利己主義者と利他主
We discussed the difference between an egoist and an altruist.
Compound of 利己 (self-interest), 主義 (principle/doctrine), and 者 (person). The term is a direct translation of the Western concept of egoism.