This is a difficult question to answer, but going by the definition of "universe" as the totality of existence, I suppose a Creator, who exists and therefore must be a part of existence, should be included. The problem being, however, is that this would make the universe circular. In order to find the origin of existence, you must look into the origin of the Creator. In order to find the origin of the Creator, you must look into the origin of existence. In the end, looking for a source brings you nowhere.
If the creator is part of the universe you have somewhat of a chicken and the egg scenario. If he is part of the universe how did he create the universe without it existing. For sure an all powerful being could afterwards choose to integrate at least partially into the universe. After all omnipotence permits everything. But it makes more sense for the so called creator to be separate from the universe originally. A 3rd party or I guess encompassing being.