Who is Kenshin based on? I've been told that Kenshin, at least partially, is based on a real life assassin. Who was he based on, and what pieces of his story are inspired by this person?
According to the author1, he is based on Kawakami Gensai, a Japanese samurai of the late Edo period, who was executed by the Meiji Government.  

Not having seen the series nor being familiarized with the Gensai's story, I cannot tell you how much of it is based on samurai's story and how much of it is fiction. 



1: *Watsuki, Nobuhiro (2003). "The Secret Life of Characters (1) Himura Kenshin". Rurouni Kenshin, Volume 1. Viz Media. p. 56. ISBN 1-59116-220-3.