If you ask this question, then you probably didn't read the manga or watch the anime. Inuyasha is a half demon- his mother was a human, and his father is a dog demon. Inuyasha was pinned to a tree by one of Kikyo's sacred arrows for 50 years. Inuyasha is 15 years old (in appearance). That is pretty much all you need to know about Inuyasha
Inuyasha is a dog-demon. He's a half-demon, actually. His father is a big and well known dog youkai (demon) and his mother a noble woman.