Ōnokuni Yasushi (大乃国 康, born October 9, 1962, as Yasushi Aoki (青木 康)) is a former sumo wrestler from Hokkaidō, Japan. Making his professional debut in 1978, he reached the top division in 1983. In 1987 he won his first yūshō or tournament championship with a perfect score and became the sport's 62nd yokozuna. However, he was able to win only one more championship before his retirement in 1991. He has remained in sumo as a coach and in 1999 became the head of Shibatayama stable.
Aoki was born in Memuro Town, Kasai District, Tokachi, Hokkaidō, Japan. At school he did judo, but after a sumo tournament in the area, he was recruited to Hanakago stable by wrestler Kaiketsu Masateru and fought his first bout in March 1978 aged 15. When Kaiketsu retired from the ring in 1981 he set up his own stable, Hanaregoma stable, and took Aoki with him.
He reached the second jūryō division in March 1982, and the top makuuchi division a year later in March 1983. He made his san'yaku debut at komusubi just three tournaments later. In November 1983, ranked as maegashira 3, he won his first special prize and three gold stars by defeating all three yokozuna (Kitanoumi, Chiyonofuji and Takanosato). This earned him promotion to sekiwake. The next March, he defeated three yokozuna and three ōzeki and won special prizes for Fighting Spirit and Outstanding Performance. He was runner-up in the July 1985 tournament, recording 12 wins against 3 losses, enough to secure promotion to ōzeki. He was runner-up again in his ōzeki debut, scoring 12-3 once more. His performance over the next few tournaments was good but not spectacular, until in May 1987 he won his first tournament title with a perfect record of 15 wins and no losses, becoming the first man other than Chiyonofuji to win a top division yūshō in the new Ryōgoku Kokugikan. After two runner-up performances in the next two tournaments, in September of that year he was promoted to yokozuna, sumo's highest rank. His three tournament record of 40 wins and just five losses tied with Wakanohana II as the best produced by a candidate for yokozuna promotion.
His first tournament as yokozuna finished with a disappointing 8-7 score, but in March 1988 he beat yokozuna Hokutoumi in a play-off to achieve his second tournament victory. However, the Kokonoe stable yokozuna Chiyonofuji and Hokutoumi were to prove dominant over the next few tournaments and he never won another tournament. He scored a famous victory over Chiyonofuji on the last day of the November 1988 tournament, however, ending Chiyonofuji's 53-bout winning streak in what turned out to be the last sumo match of the Shōwa period.
From 1989 he began to suffer from sleep apnea. He gained weight, passing 200 kg, and began to suffer leg problems. He lost some weight through a combination of training and diet, but this weakened him and he never fully recovered. He missed most of the July tournament due to a knee injury, then in September he became the first yokozuna ever to go make-koshi, or turn in a losing score of just 7 wins out of 15 bouts. He did the only thing expected of him - he offered to resign - but he was told by the Japan Sumo Association to soldier on. In his comeback tournament in January 1990 he scraped by with 8 wins but suffered a serious ankle injury and missed the next four tournaments, an unprecedented absence for a yokozuna.
He finally returned to the ring in November 1990, and scored ten wins, defeating Chiyonofuji again on the final day. In March 1991 he was runner-up for the seventh and final time in his career, finishing one win behind Hokutoumi on 12-3. His final day defeat to Kirishima handed the yūshō to Hokutoumi and robbed him of the chance of a play-off (which Hokutoumi admitted he would almost certainly have lost as he was injured in his bout the previous day). Ōnokuni missed the following tournament in May due to a fever resulting from a skin infection, and upon his return in July he was defeated four times in the first eight days. He announced his retirement from sumo at the age of just 28 after being beaten by Akinoshima on Day 8, leaving a disappointing record of just one yūshō and two runner-up performances in his 23 tournaments at yokozuna rank. Discounting the special circumstances of Futahaguro's departure from sumo he was the second youngest yokozuna to retire, after Tochinoumi.
Ōnokuni has remained in the sumo world as an oyakata, or elder, and opened his own training stable, Shibatayama-beya in 1999. In March 2008 the stable produced its first sekitori, Daiyubu, but he spent only one tournament in jūryō and retired suddenly in June 2010 after falling out with his stablemaster. Daiyubu filed a lawsuit in September claiming that he was slapped and punched, and his topknot was cut off against his will. Shibatayama was questioned by police over the alleged incidents. The case was eventually settled out of court. In March 2016 Shibatayama and one of his wrestlers, Komatokuni, were ordered by the Tokyo District Court to pay 32.4 million yen (287,500 USD) in compensation to another former wrestler who the court ruled had faced "daily abuse" since joining in 2008 and had to undergo four surgeries for a detached retina, eventually losing sight in the eye in 2013. Shibatayama appealed the ruling, and in November 2016 a court-mediated, confidential settlement was reached.
In 2013 his old stable closed when Hanaregoma Oyakata reached the mandatory retirement age, and their wrestlers transferred to Shibatayama stable. As of March 2016 the stable has no sekitori.
He also has a reputation as a baker of cakes, and published a book (第62代横綱大乃国の全国スイーツ巡業, 62nd Yokozuna Ōnokuni's National Sweets Tour).
His autobiography, titled Winning Even When You Lose, was published in 2008.
He has been married since 1989.
Ōnokuni favoured grip on his opponent's mawashi was migi-yotsu, a left hand outside and right hand inside position. His most common winning kimarite was yori-kiri, which accounted for nearly half his victories at sekitori level. He was also fond of uwatenage, or overarm throw. He had a somewhat defensive style, preferring to wait for his opportunity rather than take the initiative right from the beginning of a bout.