Rurouni Kenshin

The Rurouni Kenshin series was created by Watsuki Nobuhiro. The manga is 28 volumes long (and is currently being released in the US by Viz) and the anime is 95 episodes long. The series is made up of several major arcs: Tokyo, Kyoto, Meiji(anime only), and Jinchuu(manga only). There is also a movie, Ishinshishi no Requiem and two OAVs, Tsuioku Hen, a four part OAV, and Seisou Hen, a two part OAV.

Rurouni Kenshin is about Himura Kenshin who at the story's beginning is wondering Japan (in Tokyo atm, in the 11th year of the Meiji Era (1878) to be specific). He ends up at the doujo of Kamiya Kaoru and ends up staying there. Eventually the pair are joined by Myojin Yahiko, Sagara Sanosuke, and Takani Megumi. With this we have the main cast of the series (known as the Kenshin Gumi).

You may be wondering why Kenshin was wandering around Japan. During the Tokugawa era he was Hitokiri Battousai (if you're going 'huh what' here, basically he was an assasin for the Ishinshishi, one of the main fighting/ruling groups in Japan at this time). Many things happen during that time including the meeting of him and Yukishiro Tomoe who plays an integral part in shaping the Kenshin we know in the present day series time line. Kenshin, as one would assume, killed many people during his time as Hitokiri. Due to this (and also because of a major event/spoiler involving Tomoe) he swore to give up killing after he helped see Japan into the Meiji Era. He then began wondering Japan trying to help people in need with his Sakabatou (Reverse Blade Sword).