Who owns an academic journal? Reputable academic journals have independent editorial boards, but who owns the journal? Are they owned by academic societies, universities, academic publishers? Are there several different ownership models, and are some more common than others?
This question is distinct from the question of who owns copyright on the articles, since journals can publish some or all of their work with copyright retained by the author, or with a Creative Commons license, etc.
Most journals are now owned by one of the big three for-profits (Springer, Wiley, and Elsevier).
There are other journals that are owned by non-profits like the American association for the advancement of science (AAAS owns Science) or specific scientific societies. The American Physical Society publishes all the Physical Review journals. The American Institute of Physics does Applied Physics Letters, Journal of Applied Physics, Review of Scientific Instruments, and many others.
A few are owned by large funding bodies that are pushing some desired change to publishing (like HHMI which owns eLife). Things like arXiv are generally managed by academic institutes and funded by private money (the Simons Foundation and CZI are both big funders).
The high profitability of academic journals means that the for-profits are really squeezing the society journals, but AAAS and eLife are still doing fine.
There are some differences by field, but this applies to most STEM fields.