Asuma Sarutobi is a Jonnin level ninja and the team leader of Shikamaru, Ino, and Choji.
WARNING: Spoilers for those who have not seen Naruto: Shippuuden - The Immortals Arc
Asuma was born the son of the Third Hokage, and in later years would become the uncle of Konohamaru. He at some point in time had a falling out with his father and left Konoha to pursue his personal interests. During his absence he became one of the Twelve Guardian Ninja, a group who protected the Land of Fire's daimyo, indicated by the sash on his waist. Prior to returning to Konoha to resume active military duty, he accumulated a bounty of 35 million ryō, something he seems to be particularly proud of.
Asuma was killed in episode 80 on the Shippuuden anime. He was killed by Hidan, an extremely powerful, immortal Akatsuki that uses a long range, 3 pronged scythe. His technique allows him to "connect" with his opponent and whatever pain he endures, so does his opponent. Obviously though, however, as he is immortal, if he stabs his heart, only his opponent will die. Asuma's ghost made one final appearance when Shikamaru later avenged him by blowing Hidan up in an enormous pit, and crushing him with rocks. Asuma gives Shikamaru the Will of Fire, and Shikamaru lights Asuma a cigarette one final time.
Asuma is later one of the "noteworthy" ninja resurrected by Kabuto with the Edo Tensei. He faces off against his former students, all the while trying to provoke them into defeating him, as he is very much not in control of his actions. Eventually they overwhelm him and pin him with his own trench knives, and is sealed away to prevent further attack. When the Edo Tensei is quelled by Sasuke and Itachi, Asuma's soul ascends to heaven.
Asuma uses trench knives to fight. These knives are made of a special metal that is capable of being infused with chakra. With his Flying Swallow , he can extend the blades with his chakra to injure an enemy several feet out of the physical blade's range. When demonstrating his wind-based chakra for Naruto Uzumaki, Asuma explains that these chakra-covered blades (when utilized by someone with wind-based chakra) possess enough power to pierce through rock. During the invasion of Konoha, Asuma is able to use these blades in unison with his taijutsu abilities to single-handedly defeat nine Sound ninja without being hit once. Asuma's fighting style most resembles that of Western Boxing.
In addition to his blades, Asuma can use Fire Release: Ash Product Burning to breathe out a cloud of superheated ash capable of causing third-degree burns. Because it is ash and not flame, the attack remains in the air around the target, and therefore remains potent for a longer period of time.
Also, in most of the Naruto games, Asuma is one of the stronger playable characters. In Narutimate Accel, one of his ougis involves him using a fire technique and a lighter to create a wall of fire. He will then use a wind technique on the wall of fire to create a fiery explosion.