The early anthropologist who saw religion as rooted in a belief in spirits and the worship of them was

He was "James George Frazer".

Sir James George Frazer was a Scottish social anthropologist powerful in the beginning times of the advanced investigations of folklore and relative religion, mythology etc. He is regularly viewed as one of the establishing fathers of present day anthropology. His most well known work which he wrote in 1890 is entitled "The Golden Bough", one of the books which still provides guidelines for the researchers in the field.