Anime character from Rurouni Kenshin also known as Samurai X in the United States.
He is Kenshin's rival from back was still the Hitokiri Battousai. He was the third captain of the Japanese police force known as the Shinsengumi.
His premiere technique is known as the gatotsu. He would hold his katana in his left hand with the blade facing upwards. The right hand is almost cradling the tip. The legs are slightly bent. From this position, he can unleash a variety of attacks. The gatotsu was specifically made up for the character, but it was based off an actual Shinsengumi technique called the hiratsuki.
His personal philosophy is Aku Soku Zan which means approximately "kill evil instantly." He also smokes quite often.
He is one of the most badass characters ever created in anime. When watching this series with a group of fans, it is not uncommon for them to all cheer whenever Saitou takes up his gatotsu stance. Unlike Himura Kenshin who must always preach about how killing is wrong and blah blah blah, Saitou usually just dishes out the ass-whipping and follows it up with a snappy quote or two.
See also: Saitoh Hajime