The idea is to help writers create realistic characters by sharing an insider's view of your own particular Meyers-Briggs personality type. I'm excited to share about the INTP; partly because it's the type I understand and relate to the most and partly because it's my type so it must be the best.
One disclaimer before I begin: I don't know any other INTPs so some of the traits I'm going to share may be true only of myself. If you're an INTP and you notice any inaccuracies, that's why.
So here we go.
The INTP is one of the most insulated types, locked away in their own world of endless ideas and possibilities. Their introversion makes them focus more on what's going on inside them than what's happening around them; their intuitive side makes them more focused on future possibilities rather than present realities; their thinking side prevents them from connecting to other people on an emotional level; and their perceiving side keeps them from ever being completely certain about anything.
Consequently the INTP is a mass of contradictions and endless paradoxes, wholly unable to cope with the sheer volume of the ideas that fill their minds and always a little out of sync with what's going on in the world around them.
INTPs are, above all else, thinkers. To them it's not what you think or why you think but the thinking itself that is important. Ideas are oxygen. Descartes' famous quotation, "I think, therefore I am," fits the INTP to a T. (INTPs also tend to have a horrible taste in puns, in case you haven't noticed.)
They're very good at detecting patterns and sequences. INTPs use patterns to organise information, making it easier for them to grasp (part of the reason we're fond of stereotypes and putting people into boxes).
INTPs think so much that they often end up overthinking things. All analysis is extremely complex because every single option must be taken into account and measured against every other option. Therefore, making a decision is a huge deal for an INTP, and, once a decision is made, they'll generally cling to it stubbornly until it no longer works.
INTPs like to think deeply on important but generally impractical subjects, such as life and death, human nature, what constitutes reality, etc. They are masters of the abstract, usually choosing to dwell in the theoretical realm rather than put their ideas to practical use. They're rarely bored because their favourite thing to do--thinking--can be done anywhere anytime; in a crowded airport or on a desert island.
They DO however get bored of the outer world (normal problems and people just seem so petty), at which point they retreat to their inner mind palaces.
Like other introverts, INTPs like to be alone and tend to be total home-bodies. Part of the reason for this is that they're so absent-minded that they'll often embarrass themselves in public (Archimedes once got so excited by an idea that he ran home from the bath without his toga). Although INTPs want to be different from other people, they also hate to draw attention to themselves and, when they aren't lost in their own abstract world, tend to feel shy and painfully self-conscious around other people. (Part of this may be due to their notorious lack of fashion sense.)
Judging from the memes on Pinterest, INTPs apparently like to sleep a lot. I don't know if this is true of all of them but it's true of me, so I'll mention it.
INTPs are usually laid back, tolerant people. Their P side allows them to respect other people's opinions and helps them see issues from perspectives besides their own. They'll rarely take a hard stance on anything, except for a few issues on which they feel strongly.
That being said, there are some things that upset the INTP. One of them is control. INTPs hate to be controlled and object on principle to controlling others (although they can occasionally be manipulative).
The biggest thing that upsets an INTP however is being illogical. Logic and reason are hugely important to INTPs; they don't know how to make sense of the world without them. I often find myself frustrated by emotional arguments that have no grounding in actual reason or facts, and popular songs and advertisements grate on me (I sometimes vent my frustrations in long, internal debates with the singers).
INTPs are pretty good at argument. They generally know exactly what they think on any given subject and they know exactly why they think that. They have not only thought out all the pros of an argument but also the cons and can argue for the opposite side better than their opponent.
To an INTP the point is not to win the argument but to arrive at the truth, which requires a careful exploration of all sides of the issue. If they feel that their opponent isn't doing a good job of arguing his case, they'll step in and help him out. They don't mind losing an argument very much because to them it isn't losing if they've arrived at the truth.
With their uncanny ability to detect patterns, INTPs are good at "reading" people. They can be terrible trolls because they know what will set people off and enjoy pushing people's buttons to see what will happen.
Unfortunately, when they are actually engaged in conversation, they can be completely lost as to what a person is trying to communicate and just want to get out of the conversation as quickly as possible. They'll usually answer questions at face value because they're not sure what kind of answer the other person wants and this can cause them to come across as blunt or even rude when they really don't mean to be.
INTPs are past masters of the info-dump. They don't like not knowing something, so if you ask an INTP a question, he'll probably give you all the information he has on the subject (which might be a whole lot) in an effort to be helpful. Unfortunately, you'll have to sort through all the disorganised information and it probably won't be the information you were looking for.
INTPs think so much on so many different subjects that they have great difficulty staying on topic. They'll run off down rabbit trails and then rabbit trails of the rabbit trails. You may be so confused at the end of the conversation that you have no idea what you started off talking about, but the INTP will be able to follow all the thought threads back to the original subject.
While they think and feel a LOT, INTPs are terrible at expressing any of it (hope this post makes sense, by the way).
With their fundamental disconnect from reality, INTPs tend to be relationally challenged. They'll usually only have a small circle of very close friends and keep the rest of humanity at a distance. Getting involved in a relationship is a lot of work for an INTP and the effort of understanding something so illogical as a human being doesn't always seem worth the trouble.
INTPs are always learning and never really make up their minds completely on a subject. Partly because of this, INTPs have difficulty caring deeply about anything, whether it be principles, goals, or people. They often feel that in the end nothing really matters. So, even though they may have millions of amazing ideas that could change the world, they rarely follow through on them.
With all their distrust of emotion, INTPs can sometimes be very sentimental, although they may not want to admit it.
This may be true of only me and the twelfth doctor, but hugging is not fun. I hate physical contact of any kind (unless it's a punch in the face).
INTPs can be terrible grumps. (Especially if you wake them up.)
Supposedly Einstein was an INTP but he's not fictional so I guess I can't list him.
According to what I've found on Pinterest, some fictional INTPs are as follows:
The Twelfth Doctor (BBC's Doctor Who)
And of course these are all debatable, but although I've seen Spock listed as an ISTJ, I firmly believe he is an INTP.
INTP Problems: 24 Signs That You Are an INTP
INTJ vs. INTP: How to Tell the Difference
And in case you want some other mbti types in your story, check out these posts:
ENFP (by Gemma @ Chasing Daisies)
INFJ (by Hannah @ Hannah Heath)
ISFP (by S. M. @ Tea with Tumnus)
INTP (by Alina @ WriterAlina in which she covers everything I missed)
INTJ (by Kerry Jane @Metanoia)