The Lightning Thief
by Rick Riordan
Grover is a satyr. Satyrs are half-man, half-other creature (not always half-goat). They serve Pan, the God of Wild Places, and make it their life's work to find him (he has disappeared). Satyrs can speak to animals, and they have deep respect for nature and everything in it. You could think of them as the greatest environmentalists ever to live.