Golems are a special class of autonomous beings. By definition, golems are a collection of minerals possessed by a spirit. They are are not "alive" in the traditional biological sense, but they share many characteristics with animal life. They can "eat" minerals to grow themselves, and when large enough, they can split into two copies, effectively reproducing themselves. They also need to feed on some form of energy to keep functioning, and if they're deprived of energy for too long, they will "starve" and fall to pieces. What kind of energy they require varies based on the particular species of golem. They don't appear to age, although immortality isn't unheard of among certain regular animals as well.
Some golem species are known to have been created by wizards and other magical entities, but some golem species have been around since before recorded history. How these ancient golems came to be is not currently known.