Musashimaru Kōyō (武蔵丸 光洋), born on 2 May 1971 as Fiamalu Penitani in Samoa, was the second foreign-born sumo wrestler in history to reach the rank of yokozuna.

Fiamalu Penitani moved to Hawaii at the age of 10. Encouraged by success in Greco-Roman wrestling in high school, he moved to Japan, adopted his current name and joined the sumo world in 1989, becoming a professional in 1991.

Musashimaru's sheer 223 kilogram (492 pounds) bulk combined with 191 cm (six feet, three inches) of height made him a formidable opponent, and his fan base was helped by a surprising facial resemblance to Japanese warrior hero Saigo Takamori. He moved up the ranks quickly and earned a majority of wins in a record 52 tournaments consecutively, but was unable to gain the successive championships needed to become a yokozuna. In 1993, Hawaiian wrestler Akebono made history when he became the first foreign yokozuna; it took Musashimaru until 1999 to match the feat.

During his career he won a total of twelve top division championships, one more than Akebono, and also won over 700 competetive bouts, one of only five wrestlers to have achieved that feat to date.

In November 2003, Musashimaru announced his retirement, due to a chronic injury in his left wrist. He officially retired on October 2, 2004.