a teaching/research 'fellow' [=a graduate student who gets money in exchange for teaching/research]
He attended the concert with a 'fellow' student. [=someone who is a student, as he is]
He has always tried to be of service to 'his fellow man'. [=to other people]
(..) - Take it away. - Take it over there. And tell Luca Brasi to come in. I'm a little worried about this Sollozzo fellow. Find out what he's got under his fingernails. Go to the Tattaglias. Make them think that you're not too happy with our family (..)1972 The Godfather