Gluttony

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 Homunculus 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. In the few times that he has been alone he has been shown to be indecisive and directionless, unable to make decisions for himself. He also seems to share a close bond with his older sibling Lust whom he, prior to her death, was frequently partnered with. He did have mild awareness though and could hold a grudge, evidenced by his rage and desire to kill Roy Mustang for murdering Lust. In addition, he seemed to have a good memory, instantly remembering Lan Fan while she attacked him despite not being able to see him and quickly recognizing Edward, Alphonse and the others by scent (it is implied his memory is tied to his ability to smell).