Honinbo Shusaku was a professional Go

Go (board game)

Go , is an ancient board game for two players that originated in China more than 2,000 years ago...

 player

Go players

This page gives an overview of well-known players of the game of Go throughout the ages. The page has been divided into sections based on the era in which the Go players played and the country in which they played. As this was not necessarily their country of birth, a flag of that country precedes...

 and is considered by many to be the greatest player of the golden age of Go

Go (board game)

Go , is an ancient board game for two players that originated in China more than 2,000 years ago...

 in the mid-19th century.
He was nicknamed "Invincible" after he earned a perfect score for 19 straight wins in the annual castle games. Some say that he was not stronger than his teacher, Honinbō Shuwa

Honinbo Shuwa

Honinbo Shuwa was a Japanese professional Go player, and also the fourteenth head of the Honinbo house .His most significant games were probably the three challenge games of 1840 and 1842 against Inoue Genan Inseki...

, who by convention did not play in the castle games. In addition out of respect for the elderly teacher, Shusaku refused to play with white against his teacher thus there is no clear gauge of the difference in strength between them.