Who is Ellie from A Dog's Purpose and what is their importance?

Ellie is the main character in the third reincarnation. She is a German Shepherd. Ellie works as a search and rescue dog, first with Jakob, then with Maya. She is empathetic and affectionate with her trainers but stays true in her deep love for Ethan. During this third reincarnation, Ellie discovers that her purpose is not just to find people but to save them.