Musashimaru Kōyō is an American-born Japanese-naturalized former professional sumo wrestler. He was born in American Samoa, before moving to Hawaii at the age of 10. At 18 he moved to Japan and made his professional sumo debut in 1989, reaching the top makuuchi division in 1991. After reaching the rank of ōzeki in 1994 his progress seemed to stall, but in 1999 he became only the second foreign-born wrestler in history to reach the sport's highest rank of yokozuna. Musashimaru won over 700 top division bouts and took twelve top division tournament championships during his career. His sheer 235 kg (518 lb) bulk combined with 1.92 m of height made him a formidable opponent, and he was remarkably consistent and injury-free for most of his career. An amiable personality, his fan base was helped by a surprising facial resemblance to Japanese warrior hero Saigō Takamori. After becoming a Japanese national in 1996 and retiring in 2003, he became an elder of the Japan Sumo Association and founded the Musashigawa stable in 2013.

Makuuchi (幕内), or makunouchi (幕の内), is the top division of the six divisions of professional sumo. Its size is fixed at 42 wrestlers (rikishi), ordered into five ranks according to their ability as defined by their performance in previous tournaments.