Atreju is a male name.
Atreju is a form of the name Atréju, an invented name of the German author Michael Ende for the ten year old boy in his novel “The Neverending Story” (1979).
The book says, Atreju means “son of all”, because he was an orphan and was raised by all of the members of his village. But maybe Michael Ende was inspired by the Greek mythology. Then, Atreju means “fearless” (from Ancient Greek “atreus”).