O won the Honinbo title in 2000 and held it the following year before losing it to Kato Masao in 2002. O took the Oza title from Cho Chikun in December 2002. In July 2012, O Meien won his sixth title, the 2nd Igo Masters Cup, beating Cho Chikun.
In February 25 2010, O Meien hit the 900 landmark by beating Ko Iso in the final prelim of the 35th Kisei.
New joseki, invented by O: http://gogame.info/samples.html?id=51
O Meien's non-standard opening moves are called "meienisms".