The US statute defines an inventor as “the individual or, if a joint invention, the individuals collectively who invented or discovered the subject matter of the invention.” 35 USC 100(f).
For US patent purposes, an inventor is a natural person, and is not a corporation or sovereign. Univ. of Utah v. Max-Planck-Gesellschaft zur Forderung der Wissenschaften E.V., 734 F.3d 1315, 1323 (Fed. Cir. 2013).
Inventors are individuals that conceive of the invention. The Federal Circuit said:
“Conception is the touchstone of inventorship, the completion of the mental part of invention. It is the formation in the mind of the inventor, of a definite and permanent idea of the complete and operative invention, as it is hereafter to be applied in practice. Conception is complete only when the idea is so clearly defined in the inventor’s mind that only ordinary skill would be necessary to reduce the invention to practice, without extensive research or experimentation. [Conception] is a mental act…” Id.
The question about who owns the invention is different from who is an inventor. By default the inventor is an owner, unless by contract or law someone else is the owner, such as an employer of the inventor.