How did Hannibal become the type of cannibal he is?

It's important to understand that Hannibal Lecter is insane and is trying to reverse the death of his sister Misha. He even tries to build equations that could reverse entropy and thus the the flow of time - these calculations are described as elegant at first but quickly devolving into insanity and wish-fulfillment. He, however, believes he has found a way in Clarice Starling.

This is where the book Hannibal diverges in the extreme from the movie Hannibal:

In the final chapter, Hannibal actually keeps Agent Starling in a childlike state and helps her achieve closure over the death of her father. He uses hypnosis and narcotics, and Starling is unable to fight him and actually partakes in eating Agent Krendler's brain. After this meal, she seduces Hannibal and helps him achieve closure over the death of his sister. She asks him: "Were you ever angry at Misha because she took your mothers breast from you?" to which he replies that he doesn't remember (a probable lie). She offers him her breast and tells him that this one will never be taken from him. He accepts and they find true happiness together.

Something else the movies don't explain very well is the fact that Hannibal has been trained from boyhood in the ancient art of building a memory-palace. This is how he has achieved his photographic memory. After fifty years of practice his palace has such a greatness that he can escape into it and can resist torture by staying in his own mind.

Hannibal has suppressed the memory of eating the broth made from his sister.

However, as one of the characters he murders says: "You have to kill everyone who knows, don't you?" It would appear that he also needs to eat from the men who ate from his sister. Why the habit continues is not explained in the books nor the movies other than for enjoyment and the love of cooking.

In the narrative, he seems to find cannibalism comforting, and remember, he only eats 'the rude'. The men who ate his sister and fed her to him, were war-bitten rude men of low education. I suspect he hunts them still and will never stop. The ending of Hannibal the book is ambiguous and we only know that he shows up in Rio with Starling, and that Barney spots them and flees the country without notifying anyone. This is the terror Hannibal strikes in people. He truly is a monster and seeing him unrestrained is terrifying.

For lack of a better description, I would call him a superhero cannibal. A truly unique entity. The people who get in his way are removed but not necessarily eaten. Again the text is ambiguous. We know of many victims that aren't described very well, such as the curator who held the position he wanted and a student's body that was never recovered. Also, he didn't eat from Mason Verger - apparently he was only good for dog food.

Thus Dr. Lecter seems to have strict standards and appears to uphold them religiously within his own insane frame of reference, which is only vaguely described so far. No one knows if the tale will be continued for such is the mystery of the author, who prefers not to say anything until after the book is written.

He cannabalises because his sister was killed and cannibalised.

The official backstory of Hannibal derives from the treatment his sister Mischa received (and is explored in detail on his Wiki page). In the books, Lecter and Mischa are very close. However, to escape the war his family movie into a lodge in a forest. One day, his parents are killed, and looters invade the lodge and hold them both captive.

Mischa is killed and then cannibalised by the starving group of looters, and traumatises Lecter.

He attacks his first person at 13 (a local butcher) and then murders the man who kills his uncle, eating his cheeks (which is his first act of cannibalism). He proceeds to murder a total of nine people before he is eventually captured (which brings us up to date with the films). These nine people include all six members of the group that attacked and killed his sister.

Films

In the three films, his back story of murders is briefly described, but his reasons for becoming a cannibal aren't explored in detail.

TV Series

In the series Hannibal, we see his background from the books, albeit with some subtly different details (such as the order the men are killed). However, a young Hannibal, Mischa and all the various looters who attacked her are shown (as are their deaths).

Type of cannibal

Hannibal certainly doesn't eat people for religious reasons, or sexual satisfaction. In fact, his exact rationale isn't clear. Remember, this is a man who does not fit any known psychological profile, as the books tell us.

He seems to eat part or all of his victims for a variety of reasons, including:

1. Revenge (such as in the case of the looters)
2. Disappointing qualities (such as in the case of Benjamin Raspail, whose poor performance in the Baltimore Philharmonic Orchestra ruined Lecter's night).
3. Rudeness (such as in the case of Paul Krendler)

Ultimately, I don't think it's possible to concisely and succinctly describe the type of cannibal Lecter is, or even the type of criminal he is, as the books (and films) go out of their way to convey that he is a unique criminal who defies description.

I disagree slightly with Martin Andrew's answer on the Religious note. Religion plays a signifigant role in both understanding the character, his oragins, how he thinks, but also the series, since relgion plays a role for other characters as well.

Hannibal Rising's (novel) brilliance derives from the fact that Hannibal's origan story is born not only out of a war-torn Lithuania during WWII (a eugenics war), in which his parents become the causualty of German planes and Russian tanks, but also it's story about class warfare, as it is poorer Lithuanians that become the biggest war criminals and do the unthinkable to Misha, Hannibal's little sister---a sister Hannibal played "teacher" to...

When we see Hannibal's upbringing before the devistating event that changes Hannibal forever, readers learn he is VERY well educated. The novel, through the teachings from his Jewish teacher, takes readers on a tour of his family's prestiegious castle, in which readers learn the Lecter family are decendents of Teutonic Knights. The reason that's signifigant is because Thomas Harris is making a religious (or sacreligious) point about Lithuania's history as it's a country, once Pagen, taken over by Christian Military Order!! It's in part about about what comes around, goes around (Karma, Justice) and/or how the human condition socially includes or excludes others through one's beliefs...

"Mischa, we take comfort in knowing there is no God. That you are not enslaved in Heaven, made to kiss God's ass forever. What you have is better than Paradise. You have blessed oblivion. I miss you every day." -Hannibal Rising

Hannibal later in the novel states that he is an athiest, but this really isn't exactly true, because he basically is waging war, being on a personal crusade, towards those that accosted his sister---In the Hannibal self-titled novel, we learn Lecter is a Stephen Hawking fan believing in a (now debunked) theory of 'time moving in reverse' along with necromancy, as he is trying to alter Clarice Satrling to make her a vessel for his dead little sister's consciousness to reside in!! (A very metaphysical idea)

Hannibal's 'religious' puritan drawing of Clarice Starling, the savior of Lambs:

But furthermore all four novels are laced with various allegories, including Silence of the Lambs being specifically about the idea of a sacrificial lamb or Red Dragon getting into William Blake or Hannibal getting into Dante and Leda and the Swan. Hannibal Rising also gave Hannibal a heavy dose of Easter Philosophy through Hannibal's admiration of his exotic Japanese Aunt, Lady Murasaki...

"Hannibal at eighteen was rooting for Mephistopheles and contemptuous of Faust, but he only half-listened to the climax. He was watching and breathing Lady Murasaki..." -Hannibal Rising

Bryan Fuller's Hannibal adaptation clearly saw through and read between the lines of Harris' allegories and realized that Hannibal was not so much an athiest, but more like John Milton's version of The Devil in Paradise Lost where the idea was about taking control and defying the limitions of humanity and the nature of the universe, by deeply understanding the human condition, by playing God!!

Fuller: Hannibal is a wily guy. [Laughs] As a storyteller, I have to have an answer in reality. On one hand, I could see a version of Hannibal sneaking into Will's house with an ear on a stick and pushing it down his throat. On the other hand, as a lover of horror and sci-fi and quasi-supernatural storytelling, I love the explanation that Hannibal is a devil. But that was not Thomas Harris' intention. So, he has to have been physically able to accomplish that in some manner. If we did something where it was sort of magical, then I think we would lose our grip on reality. That's something I think is very important to maintain, out of respect for the audience and also the character and his origins. But in my mind, I love the greater mythology of Hannibal being a very punitive devil.

http://www.tvguide.com/news/hannibal-postmortem-bryan-fuller-1067011/

Many episodes in the TV series bring up God from Elliot Buddish seemingly being able to see "sinners" to James Gray's "Eye to God" mural to the church scenes at the beginning of season three that include Will Graham experiencing something akin to multiple universe and memory palace through a road not taken by seeing Abigail Hobbs--matching how Hannibal says he thinks. Also the Priest says he can see her too!!

"Yeah there is something here alright, I agree with the Pagens. The horse is divine. All beasts of burden are sacred animals. This kind of mutilation usually presents as cult activity. When an animal is sacrificed, it's presumed the power of the beast will be physically transported to whom ever is offering up the goods." - Hannibal TV Series, Hannibal - 2.08

So although Fuller downplyed the metaphysics in the interview quoted above, I think one can argue he was actually building toward it, treading a very careful line of magical realism with the possibility that it could become more metaphysical, should of he had an oppertunity to finish his version of the story.

But to better use this to answer the question, Cannibalism is part of Hannibal's dichtomoy. Thomas Harris basically was asking what is the true nature of humanity, which is, if humans are enlightened beings that can spiritually transform and rise above, or is art and civility a false facade for a more complicated game of survival of the fittest, where humans are still primal hunters or animals among ourselves?

How Hannibal attacks later in life by using his mouth and teeth is alluded to how swans attack. Hannibal observed swans with his sister at the beginning of Hannibal Rising and he later immulates them, as he at first struggles from trauma. Animals are often used in art or stories as allegories to show the nature of humanity as metaphors for any given belief systems' desired or undisired behavior/outcomes. (how 'God' wants us to be or not to be)

Hannibal is selective in whom he kills, which is usually the rude (or someone ruining art) --in it's own way, it is a Eugenics movement to cultivate a society he DEEMS WORTHY--so there is irony here given the WWII and Crusade history from which Hannibal derives. More often than not, Hannibal tends to go up against people whom are worse than he is and he also tends to protect those he either loves and/or realizes can not defend themselves or those he can see himself in. In Hannibal Rising he protects a small boy from other older larger boys trying to bully the small one. In Hannibal, he saves Starling and helps Margot Verger.