A series of ScienceFiction novels written by Gene Brewer, who also narrates the books in the first person as the protagonist, Creator/HGWells-style. The books follow the so-called "Dr. Brewer's" experiences with prot,[[note]] sic; rhymes with "oat"[[/note]] a supposedly delusional yet extremely convincing mental patient who looks like an ordinary, affable man but claims to be an extraterrestrial from a planet called "K-PAX".

The series contains four novels to date: ''K-PAX'', ''K-PAX II: On a Beam Of Light'', ''K-PAX III: Worlds of prot'', and ''K-PAX IV: A New Visitor from the Constellation Lyra''.

The first novel was fairly faithfully adapted into [[Film/KPax a film of the same name in 2001]], starring Creator/JeffBridges as the psychiatrist (renamed Mark Powell) and Creator/KevinSpacey as prot.

!!''K-PAX'' provides examples of the following tropes:

* AliensSpeakingEnglish: prot claims that English is easy to learn, at least when compared to his native language.
* ArtisticLicenseMedicine: Brewer could very likely lose his license to practice medicine with how he treats prot. For just one example of why-discussing his handling of a patient with others.
* BerserkButton: The first time prot gets noticeable angry is when Brewer tries to ask in-depth questions about the nature of crime on K-PAX.
* CrapsaccharineWorld: Brewer considers [=K-PAX=] to be one. prot describes it as a utopia with no violence or war, no hunger, no crime, no government or currency, no pollution, everyone is a vegetarian, and everyone is a scientific genius free to travel the universe as they wish. Brewer sees this as meaning they're essentially wandering nomads with no sense of love or family structure.
* CrazyConsumption
* CrazyEnoughToWork: prot's methods to cure Howie. At first Brewer muses that it makes sense to encourage an obsessive compulsive to focus on specific tasks over a long period of time. Then prot tells Howie to [[spoiler:cure Ernie of his fear of death, which he does by strangling him into unconsciousness and then reviving him, and it works]]. His final task for Howie is [[spoiler:to be ready for anything prot might request of him, eventually leading Howie to realizing obsessing over knowing everything is futile]].
* DeadpanSnarker: prot isn't very deadpan, but is ''very'' snarky.
* DrivenToSuicide: [[spoiler:Robert Porter, but he fails and the prot personality takes over]].
* GeniusDitz: prot has shades of this in the book, where tests reveal that outside astrology and physics, along with some related fields, his knowledge of other areas of study is average to non-existent.
* HumanAliens: {{Subverted}}. See StarfishAliens entry below.
* HumansAreBastards: In sharp contrast to the film's HumansAreFlawed but HumansAreSpecial stance, prot notes humans are ignorant of the damage they do to themselves, their planet and other animals, and writes in his journal that unless a radical society shift takes place he doubts the species will survive.
* LawOfAlienNames: {{Averted}}. The (uncapitalized) "prot" is a vowel ''shorter'' than its pronunciation would imply.
* LiteraryAgentHypothesis
* MaybeMagicMaybeMundane: The series and film revolve around the idea that prot could be alien or human, there's good evidence for both.
* MeaningfulName: "prot" is derived from [[spoiler:Porter, Robert's last name]].
* {{Schrodingers Gun}}: The film and book both take different stances on their evidence that prot is human or alien. The book contains more in-depth hypnosis sessions that [[spoiler:have the Robert Porter personality come out and speak to Brewer, and flashbacks show a gradual growth in the detail of the world of [=K-PAX=] as he creates it in his mind, giving strong evidence that prot is just a split personality]]. The film leaves these two points out and has a greater focus on prot's inexplicable abilities, and twice when he would be "arriving" from his faster-than-light travel there's a glare of light and a quick cut away before he appears seemingly out of nowhere, giving a stronger implication that he's an alien.
** The sequels lean in either direction, with ''K-PAX II'' presenting more evidence that prot is [[spoiler:Porter's alter-ego]], and ''K-PAX III'' making it fairly clear that he is an alien.
* StarfishAliens: Subverted. prot claims that [=K-PAX=]ians are this on their home planet, but look like the most efficient creature of the places they visit. [[spoiler:It turns out that there's a bit more to it than that]].
* SunglassesAtNight: prot, and it's {{justified}} as [=K-PAX=]ians are used to much dimmer light, so that to him Earth's sun is blinding. He never indicates any trouble seeing in the normal daytime, and takes off his shades sometimes in dark rooms when the light is tolerable for him.