American Ninja is a character from Infinity Comics.
John Stevenson fought as the American Ninja as part of a reality TV show before using his skills as an assassin. Not wanting his brother, Roger Stevenson, to know he's an assassin, John used the alias, Ed Tobias. It was Ed who killed Hattori Chiba, his family and his clan.
After Inferno exacted his revenge against Tobias, sending him to Yomi. The same demon who tried to recruit Chiba, was successful in recruiting Tobias as the Shadow Warrior.