Cao Dayuan (Cáo Dàyuán), also known as Cao Dajuan, Cchao Ta-jüan and Tsao Dayuan (曹大元, 조대원, 차오다위안) is a Chinese professional, promoted to 9 dan in 1986. He was born in Shanghai, on 26 January 1962.
He was one of the top Chinese players in the 1980s and '90s.
The list of professional players' Go styles describes his thusly:
Solid fundamentals, thick, unhurried play, a little timid but not submissive, perhaps weak at attacking. Similar to Shao Zhenzhong.
In the following list, when one event is placed after another that took place in the same year, this does not mean that it took place later.
Go Game World claim that he was runner up in the 1st Tianyuan, but this is recorded in our article as having been Nie Weiping. They also say that he won the 6th Baisheng Wire Cup (no article) at an unknown date, and also the Postal Savings Cup (also with an article), again at an unknown time.
1973: Began playing Go, at 11 years old 
1985: Runner up in the New Sports Cup (2nd time)
1985: Became a full time professional 1986: Promoted to 9p
1987: Winner of the New Sports Cup 
1987: Runner up in the CCTV Cup
1988: Runner up in the New Sports Cup (3rd time)
1988: Runner up the CCTV Cup (2nd time)
1990: Runner up in the New Sports Cup (4th time)
1991: Runner up in the Asian TV Cup
1991: Runner up in the CCTV Cup (3rd time)
1993: Runner up in the Mingren 
1994: Runner up in the Qiwang 
1994: Winner of the National Go Individual
1995: Quarterfinalist in the Fujitsu Cup
1996: Winner of the CCTV Cup
1996: Winner of the NEC Cup China
1996: Runner up in the Bawang
1998: Winner of the CCTV Cup (2nd time) 1999: Apparently given an honorary Korean 9p diploma from the KBA on 10 January. 
2002/-03: Quarterfinalist in the Samsung Cup
 Go Game World is our source for the age of 11, and might have just assumed it from the year, although with a birthday in January it is very likely anyway.
 Also sourced from Go Game World. The Guoshou tournament article doesn't list runners up. Since their claim that he was runner up in the first Tianyuan is incorrect (or misunderstood), this one should also be treated with some suspicion until corroborated.
 Suggested by the date being given on his KBA profile. The text is all in Korean, though.
His teacher was the famous Qiu Bairui, who trained many of China's strongest early professionals. Cao's own student was current top professional Fan Tingyu, as well as the less well known (but still 6p) Zhang Xuebin.
Some time in the 2000s, he authored (or at least put his name to) Middle-game Techniques, an instalment in the Master of Go series of Chinese language books.
Before 2019, he played in an event with Cho Hunhyun, apparently celebrating thirty years of their rivalry. There is a clip of the nigiri; as the Ing rules were in force, Cao apparently exercised his right as winner of the nigiri to choose the white stones (whereas most rulesets would make him take Black).
20201231天元围棋赛事直播第4届梦百合杯世界公开赛半决赛第1局：谢科VS范廷钰（曹大元、范蔚菁） -- 50m game with Chinese commentary
程晓流 围棋迷你短对局 1996年中国天元战曹大元 vs 车泽武 -- 30m game with Chinese commentary
曹大元(Cao Dayuan) 9p vs 聂卫平(Nie Weiping) 9p 第二届紫笋杯中日韩围棋元老赛决赛 (绝艺解说) -- game and variations
Cao Dayuan(1p) vs Kudo Norio(1p) - 1986-04-29 - komi: 5.5 -- a few minutes quick game playback
Cao Dayuan(8p) vs Sakata Eio(9p) - 1987-04-27 - komi: 5.5 -- a few minutes quick game playback
Korean Baduk Association (Korean, with pics)