Nagasaka Inosuke
Nagasaka Inosuke (長坂 猪之助, 1764 - 1845) was a samurai pupil of the Yasui school. Officially rated 2 dan but considered of 6 dan strength (some historians claim he was later officially promoted as such).
From June 1807 to June 1808, Nagasaka played a 21 game series against Todani Matsunosuke, the future Honinbo Jowa, winning 8 games and losing 13. It's not clear exactly what dan rank they were at the time - probably Nagasaka was at around 5 dan strength and Jowa was around 3 dan. The series began with Nagasaka taking white in each game (josen). By the 13th game, Nagasaka having fallen behind in the series 4-8, the playing conditions were changed to Nagasaka playing white in two games out of three (sen-ai-sen). These conditions held for the remainder of the series.
valerio: I collected the games of the Nijubango (source: flygo.net, Jowa's complete games) in one sgf file. Download