Sesshomaru has a very aloof personality, and only rarely does he show emotion. However, he is extremely determined and basically never gives up on anything he sets his mind to. He is also exceedingly intelligent, figuring out many of Naraku's schemes and even reaching conclusions at the end of the series for what his father intended for him. He is also very proud and arrogant; he is obsessed with power and goes to great lengths to achieve it, as his life ambition is to surpass his father in strength and battle strong opponents. In the third movie he was even prepared to fight his own father to obtain control of the swords Tessaiga and Sou'unga. He refuses to admit that anyone could be more powerful than him.
He is very cruel at the beginning of the series, since he hates humans, and even kills other demons without hesitation, often simply because they refused to move out of the way while he was walking through. However, he gradually warms up (to humans and in general) after he meets Rin and lets her follow him around and he will go to great lengths to protect her. Even though he abuses Jaken verbally and physically all the time, he trusts Jaken and protects him when he needs to. He also sometimes saves other people in the series, though this is very rare, as he gives off the vibe that he doesn't care about anybody but himself, although there are people that he does care about and he isn't always cold-hearted towards others. He saved Kagura from drowning and also protected Kagome while she was in Naraku's body.
He is still generally unsociable towards humans, though, as he blatantly ignores Miroku and Kaede and leaves in the middle of a conversation at the end of the series and after saving Inuyasha's friends from Mukotsu during the Mount Hakurei arc, rationalizes why he saved them only incidentally and how it wasn't a generous action, possibly because he doesn't want others to perceive his action as weakness. Sometimes, however, he still shows a callous side such as when he fights Naraku, not caring if everyone in the area was killed by Naraku's miasma if it meant that Naraku would be defeated by Sesshomaru's own hand. In the end, Sesshomaru is a very complex character and something of an enigma, which contributes to his high popularity with fans.