PS:I'm just copy this from shingekinokyojin.wikia.com because i want to read it to wattpad that i can read it in mobile.
Levi Ackerman (often incorrectly romanized as Rivaille) is a leading soldier in the Survey Corps, and is said to be humanity's most powerful soldier. He is also the leader of the Special Operations Squad.
Levi has short, straight black hair styled in an undercut and sharp, intimidating grey eyes. Belying his rather short stature, his physique is well-developed and heavy with muscle from extensive 3DMG usage. The slight furrow beneath his eyes are at odds with his otherwise youthful appearance. Aside from his constant frown, his expression is calm, and his unflappable demeanor oftentimes makes it difficult to guess what he is thinking.
He is most often seen in his military uniform, and wears it with the Survey Corps' green hooded cloak when embarking on extramural expeditions. When forced to take leave from his duties due to injury, Levi was seen donning a black suit, plain white shirt and dress shoes. Whether in civilian clothes or uniform, Levi is always seen sporting his trademark white cravat.
Levi is described to be a "clean-freak" by those who know him on a personal level, as he prefers his environment to be spotlessly clean. He is averse to having either his person or his equipment soiled, and has been known to wipe down his blood-smeared blades while still on the battlefield. However, he will not hesitate to touch filth if he deems it necessary. Instances of this include him rescuing a phlegm-coated Eren from the Female Titan's maw, and grabbing a subordinate's bloody hand as he comforted him during his last moments. He is always seen wearing simple white cravat, which gives him an air of being "prim and proper".
Despite this clean-cut image however, Levi has an abrasive and unapproachable personality. His manner of speaking is rarely polite, and he often makes alienating comments that are coarse or inappropriate. His dark brand of humour, always delivered in deadpan, ranges from rude to outright vulgar. He tends to phrase things in a brash and insulting manner, and is not above provoking his opponents or belittling anyone who irritates him. This often unsettles people and makes him difficult to be around.
Levi places great trust in his fellow Survey Corps members, and has proven willing to obey any order from his commander, Erwin Smith, no matter how dangerous they may seem. However, Levi's obedience is strictly limited to individuals he respects, and he has no problem showing open disdain for authority from anyone outside of this circle. At Eren's tribunal, he insulted merchants, calling them "pigs" and noting that the Military Police were not competent enough to handle Eren. It seems he also holds an open resentment for the Military Police, presumably for their constant interference and attempts to undermine the Survey Corps, and because of his criminal background before joining the Survey Corps. At one point, he mocks them by stating that they have neither battled or even seen a single Titan, and suggests that they join the Survey Corps. In the past, while Levi lived in the underground, he was a lot more rebellious, and refused to take orders from anyone, as noted by Petra Ral. However, later when he joined Erwin, he comes to respect the commander, and follows his orders because he believes in Erwin's abilities as a leader.
However, Levi has a soft side, though he rarely shows it. One of his most defining characteristics is the great value he places on preserving human life. He himself has stated that he hates having unnecessary casualties, and advises his subordinates to properly use their judgement to avoid blunders that may cost them their lives. When it was ultimately discovered that Titans may have once been human beings themselves, Levi appeared to be mortified by the news.