Honinbo Jowa (本因坊丈和, a.k.a. Kadono Matsunosuke, Kadono Jowa, or Jowa; 1787-1847) was the 12th head of the Honinbo house. He became Meijin-Godokoro in 1831. He has been noted for his extremely strong playing strength, murky origins, and infamous intrigues.
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Jowa's origins are notably murky. However, he is believed to have been born in what is now Nagano Prefecture. As was common in the Edo period, he changed his name several times. The traditional view was that he was born Todani Matsunosuke but was also called Kadono Matsunosuke and Kadono Jowa at various points. Further research highlighted by John Fairbairn now suggests much of this is, however, incorrect based upon an article by Osawa Nagahiro in the June 1989 issue of Kido. See information on Jowa in GoGoD and rec.games.go May 16, 1999 for details. He was described as being of short stature, with bushy eyebrows and full cheeks.
He appears to have been the son of a traveling merchant, but little is known about his early years. Almost no game records exist before about 1807, when he was 20 and about 2-dan. At that point he left Edo to what is now Yamagata-ken and played a 21 game series against Nagasaka Inosuke. Although Nagasaka was officially also a 2-dan, the series started with Jowa taking sen in recognition of Nagasaka's strength. Jowa forced the handicap down to sen-ai-sen.
On returning to Edo, he began to improve rapidly and made 5-dan in 1815.
After the premature death of Okunuki Chisaku in 1812, who had been the prospective heir to the Honinbo House, Jowa's chances for career progression improved. In 1819, he was recognised as Honinbo Genjo's heir and promoted to 6-dan. In the official notification however, it appears that Jowa's age is understated by 8-years and Genjo's by 2. This perhaps reflects that, at 31, Jowa was a little on the old side. He also first played in the castle games in 1819, taking Black and beating Yasui Senchi by 5-points.
Another famous jubango Jowa played was against Awano Yonezo (Shinomiya Yonezo?), a famous go gambler. To Yonezo's surprise, Genjo recommended they play with a two stone handicap (Yonezo as black) and Jowa won 5, lost 4 & 1 jigo.
Jowa and Gennan Inseki both had ambitions for the title of Meijin. A period of political struggle took place, with all the interested parties involved in different schemes. Jowa was eventually made meijin without playing a sogo against any of the other senior players. That he didn't have to prove himself over the board was thanks to Hayashi Gembi. Gembi used contacts of his within the Government to help Jowa. In exchange Jowa had agreed to promote Gembi to 8 dan upon becoming meijin.
Jowa never fulfilled this secret promise, angering Gembi. Gennan Inseki and those close to him were also outraged at Jowa's successful scheming. However the title of Meijin Godokoro was effectively a non-playing title. This meant that they had little chance of proving over the board that Jowa was not worthy of the position. Their one chance came in the famous Blood Vomiting Game when Jowa was maneuvered into playing the rapidly improving Akaboshi Intetsu. To have lost to Intetsu, several ranks Jowa's junior, would have had implications upon Jowa's status. The game initially swung Intetsu's way, but Jowa managed to salvage a win. Tragically, whether due to the effort of the game or not, Intetsu died shortly after being beaten by Jowa.
After his contacts had died, Gembi eventually revealed the secret agreement he and Jowa had made and the bakufu officials forced Jowa into retirement in 1839.
Jowa's two largest strengths were his ability to readout even the most complex situations to the end and discover profound or sharp moves in the process. He played a style of power go that often lead to complex fighting and multi-group life and death situations. The threat of capturing races and ko fights loomed constantly, esp. in his handicap games. This could lead to spectacular reversals, sacrifices and trades. He disliked running with weak groups so attacked problems head-on with powerful responses that could often overpower the opponent. The result made Jowa one of the most powerful fighters in go history.
However, his reading wasn't just for middle game fighting, but extended into the endgame. This was due to the fact that in his games groups often remained unsettled or contained residual defects entering into the endgame.
He was also a master of rescuing weak groups. In fact, Segoe Kensaku, 9d recommended amateurs not to study Jowa's games, because the way he could rescue lost causes made the games too difficult to learn from.
In his attempt to find josekies that catered to his play style, Jowa innovated several variations. He preferred outcomes stressing outward influence, attacking potential and complications.
Jowa was said to have "superhuman strength without equal" (怪力無双). Historically he was accorded the title 'latter sage' to match Dosaku (who was known as the 'former sage'). At some point in the Meiji era this title was transferred to the more wholesome Shusaku. 
The book Zain Danso contains a passage attributed to Jowa about go improvement. The original Japanese text is as follows:
|1807-10-15||Nagasaka Inosuke||Go World Iss. 16|
|1814-09-04||Hattori Rittetsu||Go Review Jul. 1970|
|1814-10-23||Hattori Rittetsu||Go World Iss. 100|
|1820-05-21||Yasui Chitoku||Appreciating Famous Games, Go Review Jan. 1968|
|1821-01-02||Shinomiya Yonezo||Go World Iss. 33, Masterpieces of Handicap Go Vol. 2|
|1821-03-05||Shinomiya Yonezo||Masterpieces of Handicap Go Vol. 2|
|1821-12-11||Inoue Ansetsu||Go Review Jun. 1970 & Autumn 1974|
|1822-04-26||Toyama Sansetsu?||Go Review Apr. 1970|
|1822-12-29||Inoue Insa Inseki||Appreciating Famous Games|
|1823-07-09||Kisohachi?||Masterpieces of Handicap Go Vol. 1|
|1831-10-19||Kato Kosaburo?||Masterpieces of Handicap Go Vol. 2|
|1835-08-13||Akaboshi Intetsu||Brilliance: Jowa's 'Ghost Moves' Destroy Intetsu, Go Review Dec. 1967, Invincible: The Games of Shusaku|
|1845-03-24||Kozu Hakuta?||Masterpieces of Handicap Go Vol. 2|
|1847-03-29||Yasuda Shusaku||Invincible: The Games of Shusaku|
 Go World, Iss. 33 p. 52
 As described in the Mindzine article, "Honinbo Jowa - Sage or Scoundrel": http://web.archive.org/web/20110512210728/http://www.msoworld.com/mindzine/news/orient/go/history/jowa.html.