The basic meaning of "Ryu-oh" is a "promoted rook". It can move as either a rook (hisha 飛車, lit. flying chariot") or a king (gyokushō 玉将, lit. "jade general") during a turn, and is one of the two most powerful pieces in shogi.
"Ryu-oh" also refers to the annual Ryu-oh Tournament (Ryūō-sen 竜王戦) sponsored by the Yomiuri Shimbun as well as the title awarded to its winner. The Ryu-oh Tournament, which is one of the seven major professional shogi title matches, was first held in 1988. It comprises preliminary tournaments in six classes and one final. The final tournament, which determines the challenger, involves competitions among eleven players (the top five players from 1st class, top two from 2nd class, and the top four from 3rd, 4th, 5th and 6th classes). The first player to win four out of seven championship games becomes the new titleholder. This title should not be confused with that of "Amateur Ryu-oh" which is awarded each year to the winner of the Amateur Ryu-oh Tournament.
Cash prizes are ¥32,000,000 for the winner of championship and new Ryu-oh titleholder, and ¥8,000,000 for the loser (approximately US$320,000 and $80,000 respectively). Additional compensation includes ¥14,500,000 for the previous titleholder and ¥7,000,000 for the challenger (approximately US$145,000 and $70,000).
"Lifetime Ryu-oh" ("Eisei Ryu-oh") is the title awarded to a player who wins the championship five times in a row or seven times in total. Active players may qualify for this title, but it is only officially awarded upon their retirement or death. (posthumously). 
The only player to qualify for the Lifetime Ryu-oh title to date is Akira Watanabe; he won the championship nine times in a row from 2004 to 2012, and will be designated at "The First Lifetime Ryu-oh" upon his retirement or death.
|1||1988||Akira Shima||4-0||Kunio Yonenaga|
|2||1989||Yoshiharu Habu||4-3||Akira Shima|
|3||1990||Koji Tanigawa||4-1||Yoshiharu Habu|
|4||1991||Koji Tanigawa||4-2||Taku Morishita|
|5||1992||Yoshiharu Habu||4-3||Koji Tanigawa|
|6||1993||Yasumitsu Sato||4-2||Yoshiharu Habu|
|7||1994||Yoshiharu Habu||4-2||Yasumitsu Sato|
|8||1995||Yoshiharu Habu||4-2||Yasumitsu Sato|
|9||1996||Koji Tanigawa||4-1||Yoshiharu Habu|
|10||1997||Koji Tanigawa||4-0||Keiichi Sanada|
|11||1998||Takeshi Fujii||4-0||Koji Tanigawa|
|12||1999||Takeshi Fujii||4-1||Daisuke Suzuki|
|13||2000||Takeshi Fujii||4-3||Yoshiharu Habu|
|14||2001||Yoshiharu Habu||4-1||Takeshi Fujii|
|15||2002||Yoshiharu Habu||4-3||Takashi Abe|
|16||2003||Toshiyuki Moriuchi||4-0||Yoshiharu Habu|
|17||2004||Akira Watanabe||4-3||Toshiyuki Moriuchi|
|18||2005||Akira Watanabe||4-0||Kazuki Kimura|
|19||2006||Akira Watanabe||4-3||Yasumitsu Sato|
|20||2007||Akira Watanabe||4-2||Yasumitsu Sato|
|21||2008||Akira Watanabe||4-3||Yoshiharu Habu|
|22||2009||Akira Watanabe||4-0||Toshiyuki Moriuchi|
|23||2010||Akira Watanabe||4-2||Yoshiharu Habu|
|24||2011||Akira Watanabe||4-1||Tadahisa Maruyama|
|25||2012||Akira Watanabe||4-1||Tadahisa Maruyama|
|26||2013||Toshiyuki Moriuchi||4-1||Akira Watanabe|