Someone just did a quantitative analysis of Captain James T. Kirk, going through all the episodes of the original Star Trek, and rather than being the promiscuous and reckless character parodied in Futurama‘s Zapp Branigan, he turns out to be a lower key and far more cautious figure:
We reach the point of no return when the omnijerk (really I suspect there’s just one vast eldritch horror sitting in another dimension that extrudes its thousand tentacles into our own, and that each one of This Guy is merely an insignificant manifestation of the beast: they couldn’t all be so boring in precisely the same way by chance, surely) decides to voice some Dinner Party Opinions on original-series Star Trek. God knows why. It’s not five seconds before he’s on ‘Kirk and the green women’. He’s mocking the retrosexist trope, but smiling a little weirdly while doing it. His own insufficiently private enjoyment is peeking out, like a semi-erection on his face. A sort of Mad Men effect: saying, “isn’t it awful” and going for the low-hanging critical fruit while simultaneously rolling around in that aesthetic and idea of masculinity. Camp, but no homo!
“You’re thinking of Pike,” I say. “The captain in the unaired pilot. Some of that footage got reused for a later story, which made Pike into a previous captain of the Enterprise. And it never actually happened—it was a hallucination sequence designed by aliens who didn’t know what they were doing in order to tempt Pike. He rejected it.”
His [the loudmouthed boyfriend of a girl invited to the party] was a common enough error, and he can claim neither the credit nor the blame for the invention. The pop culture idea of Kirk, Captain of the Enterprise for the first Star Trek series (ST:TOS) and the original run of films, has become almost synonymous with Zapp Brannigan from Futurama. To quote Wikipedia,
[t]hough famed for his bravery and strategic genius, it soon becomes very apparent that [Brannigan] is sexist, vain, and often very cowardly and inept. […] Brannigan is also completely indifferent to military casualties. […] He is arrogant, completely incompetent, chauvinistic, and stupid.
Brannigan is supposed to be part comic exaggeration of the “real” Kirk, part reflective take-down of the source character  . Per wiki, in some ways the ultimate aggregator of the vox populi, “Kirk has been noted for ‘his sexual exploits with gorgeous females of every size, shape and type’ ; he has been called ‘promiscuous’  and labeled a ‘womanizer’  .” (Note all those still-working footnotes for fan-publications and major papers and entertainment news sites.) The article “Captain Kirk’s 8 Most Impressive Love Conquests” gives us such bon mots as these:
For three glorious seasons, Star Trek‘s Captain James T. Kirk boldly seduced and explored women no Earth-man had been with before. Well, okay, some of them were from Earth, but Starfleet’s greatest discovery was that no women anywhere in the cosmos could resist the intense gaze and oft-exposed, tanned pecs of the Enterprise’s head honcho. Who can blame them, really? Of the many, many seduction [sic] committed by James T. Kirk, here are the 8 most impressive (not most exotic, which would totally include the green Orion Slave Girl, but this doesn’t, because Kirk had no problems getting under her Orion’s belt), which deserve to be recorded in the Captain’s Log for all eternity.
What follows is an inventory of Kirk’s actual behavior, which is far milder, particularly by the standard of 1960’s television, than I recall:
Let’s start, as people so often do, with those infamous Green Women.
Yes: one existed in ST:TOS. Sort of. It was a vision. On a planet Kirk wasn’t even on. A captain was there: it wasn’t Kirk. Captain Pike and this green, Orion woman  could literally never have done the deed .
(ADDENDUM: I should also mention here the first and only actual Orion woman we see in TOS, Marta: an inmate of an asylum who attempts to seduce a suspicious, wounded Kirk, who is himself interested in escaping dangerous captivity. She then immediately tries to murder him. Ah, l’amour.)
Over the course of three seasons and six films (though I hesitate to mention the films in the same breath as the series, because even the initial run of films represents a significant, reflexive re-working of the original material), we do meet some women Kirk has had romantic relations with. These previous relationships mostly seem of a type.
- Ruth (“Shore Leave”) was a college girlfriend of Kirk’s while he was at Starfleet Academy. The script implies she was also in Starfleet. We see only a facsimile of her.
- Dr. Janet Wallace (“The Deadly Years”) was a biologist, and she and Kirk broke up in favour of their respective careers.
- Janice Lester (“Turnabout Intruder”) was a Starfleet-trained scientist. Their relationship lasted at least a year, and was strained and broken by Janice’s violent resentment of Kirk’s ability to benefit from institutional sexism (check the tapes, I’m not exaggerating, that’s what she says).
- Areel Shaw (“Court Martial”) was a dedicated JAG attorney.
- Carol Marcus (The Wrath of Khan), retconned into the history of Kirk’s life by the films, was a brilliant, ground-breaking scientist. In one draft of the script, this character literally was the aforementioned Janet Wallace 
At some point during his time at the Academy, Kirk “almost married” a blonde lab technician (“Where No Man Has Gone Before”). It seems probable that she was one of the aforementioned women (all of whom but Lester were blonde, though dye exists, and all of whom but Shaw were scientists, though majors can change—I know an attorney with a biology degree myself).
With the exception of Lester, all Kirk’s relationships that we’re aware of seem to have ended amicably. He and the women involved have often kept up communication to some extent, despite the impediments caused by interstellar travel (Wallace, Marcus). The relationships all seem to have been of some duration, and characterised by fairly serious involvement on both parts. They were distinctly emotional affairs, and no one accuses Kirk of having “womanised” during them. They all involved competent people drawn to demanding, intellectually stimulating fields—usually science—and the service of something greater than themselves—almost universally Starfleet.
Kirk’s storied history of womanising seemingly consists of his having seriously dated a fairly small number of clever women in Uni. We’re even told Kirk had to be manipulated into paying attention to matters of the heart and/or loins during that period (and that Kirk’s into “longhair stuff” like 17th-century philosophy):
A tumblr fan essay  puts it well:
Nearly every instance of Captain James T. Kirk seducing an alien woman was not because he’s some randy alien shagger extraordinaire, but because he needed to distract the enemy of the given episode in order to save the Enterprise. In the same way we wouldn’t say a woman who uses her sexuality as a weapon (flirting with the villains to distract them and ultimately defeat them) is just some intergalactic bed hopper, neither is Kirk.
Masculinity is not a fixed construction: it evolves over time. When we view Kirk as Zapp Brannigan, actually we’re retconning a more current understanding of the male action hero and superimposing it over an era where it doesn’t have all that much business being.
So, Kirk is not the compulsive womanizer that we recall him to be.
You should read the rest, it is a long and well worth the read essay, but it makes clear, with extensive citations, that our image of Kirk is not a reflection of the character in the original series, but rather a reflection of the overtones that we have assigned, and his risk taking occurs only when there is no alternative.
Read it, and expect to lose a bit of your childhood in the process.
It’s worth it.