In the video game industry, the maker of the game is the developer. The one who puts the game out to the public is the publisher. Why does this matter? In general, when a contract is signed between the developer and the publisher, they work together on their respective responsibilities. However, the publisher may end up with a lot of control and power about the game. A good example would be for the game The Last of Us, Naughty Dog is the developer, and Sony Computer Entertainment is the publisher.
The short answer regarding this is contracts. Generally, before the game is completed, a developer and a publisher enter into a contract that says who has what responsibilities, and who signs over what rights. The developer may have certain rights and responsibilities that it must deliver, and so does the publisher. Sometimes these responsibilities will need approval from the other party.
But why does the developer need to sign over rights in the first place?
In copyright law, the owner of the work (in this case, a video game) is usually the creator unless there is an agreement that states otherwise. In this case, the developer would own the software, and the software would gain copyright protection (copyright protection is automatic). Some of those copyright protections include the right to reproduce the work, the right to distribute the work, and more. Since the developer is the one with those rights, it must give the publisher those rights in order for the publisher to distribute the work to the public!
That’s the simple explanation, but this does not contain all the answers and it may not be the case for every single scenario. Please, read through your contracts, and do not be afraid to get an attorney to help you if you have any legal questions!