From the given options, select the one that rightly substitutes the given expression:

One who has a charitable attitude towards his fellow beings

Philanthropist

The word that rightly substitutes the given expression is philanthropist.

• Anthropologist is a person who studies human beings and their cultures.
• Philanthropist is a person who donates money or time to help others.
• Mercenary is a soldier who fights for money.
• Philosopher is a person who studies the nature of reality and the meaning of life.

Philanthropist is the best fit because it conveys the idea of someone who is generous and giving, and who wants to help others. The word comes from the Greek words "philos," meaning "love," and "anthropos," meaning "human being."