Torah.org has excerpts from Rabbi Aryeh Kaplan’s essay. According to Rabbi Kaplan it is a three-way machlokes Rishonim:
1. R’Chasdai Crescas holds that there is intelligent life on many other worlds (that is how he understands the Gemara in Avoda Zara 3b).
2. Rabbi Yosef Albo (baal sefer HaIkarrim) holds that only human earthlings are intelligent life.
3. The Sefer Habris holds there is intelligent life elsewhere but they do not have free will. Only humans have free will.