This is usually either the author(s) or their employer(s), which may in some cases be government (or non-governmental) entities for whom special copyright conditions apply.
Most commonly, if you work for a university or other academic institution, you will own the copyright in any academic content you write and submit to a journal. If you work for a government agency or private commercial entity, your employer may own the copyright in any work you produce.
If you are not sure who owns the copyright in the submitted work, it’s a good idea to check your employment contract or speak with your employer about copyright ownership of content you have produced during or for the course of your employment.