He is a famous philosopher, influencing many people.

He is a famous osteologist, studying many fossils.

I am majoring in econometrics at university.

He is known as an expert in palaeoclimatology.

He is writing a thesis on fluid dynamics.

This ancient proverb, 'know the other side and yourself, and you will not be in danger in a hundred battles', teaches us the importance of understanding ourselves and others.