Gluttony

Gluttony (グラト二ー, Guratonī) was the second Homunculus to appear in the series, typically being in the company of Lust.

Personality
Gluttony, although under normal circumstances is quite docile, is easily prone to bouts of frenzy in which he uncontrollably tries to eat whatever crosses his path, usually someone he has been given permission to eat; which as a result, in both the manga and anime, causes him to frequently ask Lust (or any other Homunculi that he is partnered with) if he can eat them beforehand. He even asks this question to the people he is fighting at that moment. He particularly likes eating people and even mentions to Wrath that he prefers eating girls (as he finds them soft and tasty). Despite his hunger-fueled moments of frenzy, Gluttony is very childlike and is surprisingly kindly, demonstrating several times a great love for his siblings (greeting the reborn Greed enthusiastically and showing immense sorrow upon word of Lust's death) and even respects Edward Elric's request for him not to eat Ling Yao. Gluttony also does not appear to share any of his siblings' disdain for humans, and appears to be unaware that the people he eats die permanently. Because of his childishness, lack of self-control and apparent innocence, Gluttony's intelligence is thus limited in regards to usefulness for his siblings and thus has to be 'babysat' by his more aware siblings. He also seems to share a close bond with his older sibling Lust whom he, prior to her death, was frequently partnered with.

Powers and Abilities
True to his name, Gluttony is incredibly voracious, and seemingly unable to ever satisfy his hunger. However, his eating abilities vary between the anime and manga. In the 2003 anime, he can simply eat anything using his powerful jaws and acidic saliva. He also shows great strength and some skill in fighting, capable of disarming a skilled martial artist like Alphonse and even giving Scar some trouble.

In the manga, Gluttony is actually a false Gate of Truth which he can activate at will. When activating his gate, Gluttony's stomach and lower jaw opens up, revealing a large eye at its center and his ribs spread out to act as a border for the gate, doubling as extendable teeth. In this state Gluttony can consume everything in his gates eye's field of vision in an instant, which are then transported to an alternate dimension within himself. This endless space exists between reality and non-reality, and is filled with a shallow sea of blood littered with artifacts and remains of the things he has consumed, even the remains of alchemic reactions. The manga and 2009 anime version also shows a highly developed sense of smell allowing him to track his targets with considerable accuracy, even allowing him to fight in the dark (although a bit clumsily).

In the Manga & 2009 anime
Gluttony is the sixth Homunculus created by Father (according to Perfect Guidebook 2) and the failed product of Father's attempts to create a Gate of Truth. Gluttony first appears in the series in the second chapter of the manga, being confronted by Father Cornello alongside Lust. As usual, Gluttony asks if he can eat him now that Cornello is useless to the homunculi. Lust refuses, but he ignores her, possibly thinking it made little difference. He participates in the battle with Scar, having being able to detect "an Ishvalan cloaked in the stench of blood"- another of his own unique abilities. Sadly for him, Scar escapes, so Gluttony cannot eat him. Later, Gluttony is present in Father's lair when Greed is captured, who snidely remarks to Gluttony that he has not lost any weight, though Gluttony doesn't seem to mind, and is later honored as one of Father's loyal children.

When Envy recognized Number 66 from the penitentiary attack, he and Gluttony are sent by Lust along with Barry the Chopper's reanimated body to kill the traitor, inadvertently falling into the trap set up by Roy Mustang, and Gluttony is forced to engage in a fairly unsuccessful battle, being reprimanded by Pride towards the end, and told to leave the scene. While this is going on, Lust is killed by Mustang, something an unhappy Gluttony doesn't find out until later.

After another battle with the Elrics, Gluttony is captured by them with the help of Ling Yao and taken away with Hawkeye's help to a small building outside Central. Realizing that Mustang is present, Gluttony seeks vengeance for Lust's death, and opens his gate, breaks free, and tries to use this form to consume Roy Mustang, though he makes the mistake of eating Edward Elric, Ling Yao and Envy instead, trapping them in the alternate dimension within himself. Hoping to make it up to Father, Gluttony takes Alphonse Elric to see him. In Father's inner sanctum, Envy, Ling, and Ed burst out from Gluttony's stomach after Ed used Envy's Philosopher's Stone to perform a reverse human transmutation on himself to reopen Gluttony's gate. In the ensuing battle Gluttony runs out of energy and he is no longer able to revive himself. Father takes and reabsorbs what remains of Gluttony's Philosopher's Stone, promising to restore him with his memories intact. Some time later, Father recreates Gluttony by allowing him to grow off of his own body.

After returning to life, he assists Pride in kidnapping Al by tracking his scent. After doing battle with Greed/Ling Yao and Lan Fan, Gluttony becomes severely weakened once again, "dying" several times. Pride, also injured and fearing eradication, realizes that Gluttony became more of a hindrance long ago, and callously eats his Philosopher's stone to gain more energy in addition to his sense of smell. Gluttony's last words were him calling out for Lust to save him, saying that it hurts. Gluttony is the second Homunculus to die permanently (after his former partner Lust).

In the 2003 anime
In the first anime, Gluttony's personality and appearance is identical to that in the manga, but his origins are altered. He is not a false Gate of Truth, and as such he cannot open his ribcage and swallow anything quite so easily. Of the seven Homunculi, Gluttony is the least developed, and almost nothing is known of his presumed previous life as a human. As mentioned in episode 50, Gluttony was created by Dante for the purpose of manufacturing the red stones, as the souls of the people he eats will be condensed into such. He is one of the older Homunculi, being older than the current Pride, Lust, Wrath, and Sloth, but is younger than Envy and Greed. Of his siblings, as in the manga, it is Lust whom Gluttony cares about the most, much more so even than in the manga, and almost always appears alongside her, willing to do exactly as she says. Gluttony suffers from the constant desire to eat, which may contribute to his supposed desire to become human. After Lust's death, Dante transforms Gluttony into a mindless eating machine because his moping over Lust's death was annoying her and that it was starting to cause his desire to eat to recede, an act that ultimately backfires when he eats her. He appears again in Fullmetal Alchemist: Conqueror of Shamballa, having transformed into a large, multi-limbed monster since his appearance in the anime, apparently due to eating dirt or devouring Dante and the large amount of stolen lives within. Gluttony, even since being turned mindless by Dante, still holds enough recognition skills to exclusively attack Wrath (Lust's killer) during the movie, giving Alphonse Elric an easy opportunity to use Gluttony to create a gate to the other world. Although he is still transmuted, he is shown to have become quite formidable, and almost defeated Wrath. He and Wrath die at the same time and are the fifth and sixth of the Homunculi to die.

Trivia

 * A recurring theme throughout the series is that, whenever Gluttony is in a battle, he is killed an inordinate number of times in quick succession. In fact, if one includes the time he was reborn, Gluttony has died more than any Homunculus in the series.
 * Ironically, Gluttony meets his end being eaten by another, his eldest brother Pride. He is the second Homunculus to be killed by another of his kind, the first and third being Greed. However, while 'dead' in the human sense of the word, Pride (and likely Father and the other Homunculi) believed that two Homunculi simply became one again.
 * Through the course of the second anime, it has been demonstrated several times that despite Gluttony's size, shape, and weight, he holds a fair amount of agility, although he is still pretty uncoordinated.
 * Gluttony being eaten by Pride can be seen as a reference to Dante's Inferno, where the gluttonous are continually tortured by being eaten by Hell's guard dog Cerberus.
 * Gluttony was voted as the 27th most popular character in a recent fan poll, making him the fifth most popular Homunculus.
 * In the Conqueror of Shamballa movie, Gluttony's form makes reference to the three-headed worm like monster, Cerberus, from the Divine Comedy in the chapter Canto VI. The monster was a worm-like monster with three heads that also ate dirt as well as the Gluttonous, surviving in a place with nonstop storms and rain.
 * Whenever Gluttony activated his Fake Gate of Truth in the 2009 anime and manga, he was always very angry (not counting the time his Gate was forced open by Ed for Ed, Envy and Ling's escape). Whether this is a coincidence or his anger is a necessity to activate the form is unknown.
 * Gluttony and Sloth both share the same type of eyes; rather than an iris or a normal shape, they are very tiny and blank in color. Both Homunculi are also the two least mentally capable.
 * Gluttony's Japanese voice actor in the 2009 anime series, Tetsu Shiratori, previously voiced Kain Fuery in the 2003 series.
 * In both the manga/Brotherhood and 2003 anime storylines, Gluttony was created specifically to be used as a means to an end, but winds up being unsuccessful in both cases.
 * Father created Gluttony in the hopes that he could somehow bypass the Gate toll by creating his own door. Instead, Gluttony's Gate was not a true Gate, and led to another, entirely separate void plane of existence, unrelated to Truth's domain.
 * Dante made Gluttony with the intent of having him consume red water and human flesh and allowing it to condense into a Philosopher's Stone inside his body, thus bypassing the need for alchemy and the risks that came with it. (This is also why she made him such a simpleton and made it possible to take his mind away; such a tool doesn't need intellectual depth, it just needs to be hungry.) Although she didn't succeed as hoped, she was still able to use him to condense Al's Philosopher's Stone body down to a more manageable size without using alchemy and wasting the stone's power.
 * Due to his mental capability, Gluttony is often paired with his fellow Homunculi; first and longest with Lust, then with Wrath, and lastly, Pride.