Under older U.S. case law, an inventor is the one with "intellectual domination"[1] over the inventive process and not merely one who assists in its reduction to practice.
In the contemporary U.S. patent law inventor is defined as the person, who "conceived a claim".
The persons who only made prototypes or suggested improvements not claimed in a patent are not inventors.
Indeed, "[f]or the purposes of proceedings before the [EPO], the applicant shall be deemed to be entitled to exercise the right to the European patent".
To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries.
(emphasis added) This clause has been traditionally interpreted as that exclusive right to an invention is originally vested with the individual inventor(s).
Therefore, conception and "intellectual domination" over an invention is important and "reduction to practice, per se, is irrelevant.
For example, in 1991, consumer group Public Citizen sued the owners of the patent for use of the anti-retroviral compound AZT against HIV Aids, Burroughs-Wellcome.
[12] The plaintiffs claimed that several persons at the National Institutes of Health (NIH) who had contributed to the patentable subject matter were not named as "inventors.
"[13] Controversially, the courts ultimately ruled that the original patent was valid, and no error had been made in excluding the NIH researchers whose work only 'confirmed' the invention.
[14] Generally, conception is "the complete performance of the mental part of the inventive act", and "the formation in the mind of the inventor of a definite and permanent idea of the complete and operative invention as it is thereafter to be applied in practice.." (emphasis added).
Failing to name, or incorrectly identifying inventors, with deceptive intent, can result in a patent being held invalid or unenforceable for inequitable conduct.
[18] In a recent patent application, the USPTO rejected artificial intelligence machines as inventors, but has also sought comments from the public.
The inventor may license a patent to another entity for an up-front fee, an ongoing royalty or other consideration.
Henry Woodward, for example, sold his original US patent on the light bulb to Thomas Edison who then developed it into a commercially successful product.