C-3PO frequently speaks of “the Maker.” Is this a true droid religion, or is this a religious reverence by droids for their specific creators (in this case, Anakin, even though C-3PO has forgotten who he is)? Is this even a droid thing or is it just C-3PO? What else do we know about this “Maker”-worship?
Out of universe, it's George Lucas(!), at least according to his fans and followers:
Little did I know that before the final prequel film was released, I would move to Northern California and begin work on Star Wars: The Clone Wars, right alongside “the Maker” George Lucas.
In-Universe, there's a reference in the EU sourcebook "Scavenger's Guide to Droids" that indicates that the story of the Maker is something of a droid legend.
The origin of droids is lost to the mists of history. Some droids believe the story of the Maker. Creator of the first droid, the Maker pushed droids from simple machines to intelligent creations. Some droids hold that the Maker was the first droid. These conflicting views sometimes cause unrest among the droids that believe in the Maker. Nothing more than spirited debate comes of it, but of the galaxy's war-torn sectors know the destruction that can result from fervently held beliefs.
In at least one instance, C-3PO refers to Anakin as "the maker". In the formerly canonical book The Rise and Fall of Darth Vader, Anakin and Padmé arrive at the Lars homestead. C-3PO hasn't seen Anakin in over ten years, and doesn't recognize him at first; when he finally does, he says:
“The maker! Oh, Master Ani! I knew you would return. I knew it! And Miss Padmé. Oh, my.”
Earlier in the same book, he refers to Anakin as "my maker":
“Master Anakin, you are my maker, and I wish you well. However, I should prefer it if I were a little more... completed.”
However, it is worth noting that in both cases, the term is written "maker", as opposed to "Maker". You can attribute as much or as little significance to this as you like.