Gakuto Oshiro (大城 ガクト, Ōshiro Gakuto; born July 4, 1973), better known as Gackt (stylized in all caps), is a Japanese singer-songwriter, musician, record producer and actor.

Born in Okinawa to a Ryukyuan family, Gackt learned the piano at a young age and was raised on classical music and enka before becoming interested in rock music while attending high school. He has been active since 1993, first as the frontman of the short-lived independent band Cains:Feel, and then from 1995 the now-defunct visual kei rock band Malice Mizer. Gackt started his solo career in 1999 with debut mini-album Mizérable and first full-length album Mars (2000). He has released nine studio albums and, with forty-eight singles released, holds the male soloist record for most top ten consecutive singles in Japanese music history. They are mostly conceived around two conceptual stories "Moon Saga" (Moon, Crescent, Diabolos, Last Moon) and "Requiem et Reminiscence" (Rebirth, Re:Born) which are performed live in uniquely elaborate concerts. His single "Returner (Yami no Shūen)" (2007), is his first and only single to reach the number one spot on the Oricon charts. As a solo artist, Gackt has sold over 10 million records. In 2007 became a founding member of S.K.I.N., a Japanese visual kei rock supergroup, and in 2010 formed his own band project Yellow Fried Chickenz.

Besides being established in the modern entertainment industry and considered a pop icon, Gackt's music has been used as theme songs for video games (Dirge of Cerberus: Final Fantasy VII), video game films (Dragon Age: Dawn of the Seeker), anime series/films (New Fist of the North Star, Mobile Suit Zeta Gundam, Texhnolyze and Trickster) and television series (Kamen Rider Decade). In addition to his music career, Gackt has voice acted (including characters inspired by him in video games like in Bujingai and Genesis Rhapsodos in Crisis Core: Final Fantasy VII), and live acted in a few films, including a film he wrote, Moon Child, his international debut Bunraku, Japan Academy award nomination performance for Best Actor in Fly Me to the Saitama, and TV series most notably as Uesugi Kenshin in the NHK drama Fūrin Kazan. He also performed live in theatre stage plays, Nemuri Kyoshiro Buraihikae and a duology he has written, composed, and directed Moon Saga: Mysteries of Yoshitsune I & II. He also provided the voice samples for Internet Co., Ltd.'s first Vocaloid, Gackpoid.

Gackt was born on July 4, 1973, as the second of three children in a Ryukyuan family, in Okinawa of the Ryukyu Islands, Japan. His father was a music teacher, who primarily played the trumpet, and his mother was also a teacher. Gackt has an older sister and a younger brother. He lived in Okinawa until he was 7 years old (with short periods when was 16 and 26), because of his father's job, living in many different cities on Honshu and Kyushu islands in addition to Okinawa: Yamaguchi, Fukuoka, Shiga, Osaka, and Kyoto. He studied in the Moriyama High School in Shiga, and was enrolled in the Kyoto Gakuen University.

Gackt's musical education began at age three when his parents initiated his classical piano education. At age seven, continuing his classical piano education became more difficult because of time spent at elementary school and the repeated change of instructors due to relocating from city to city. It would take another four years until his parents allowed him to quit lessons. However, after losing a piano competition to a boy he met in the middle school, Gackt voluntarily returned to his piano studies, even writing orchestral scores. He has credited the classical pianist and composer Frédéric Chopin with being "the one who taught me the beauty, depth, fun, sadness, the kindness of music; that music could grant people courage, and the meaning of the layers of sound. It isn't an exaggeration to say Chopin is the foundation of my music". Since his father played the trumpet, Gackt is also familiar with brass instruments. Having only listened to classical music and enka while growing up, he did not become interested in rock music until high school, and went on to master modern percussion.

In the early 1990s, Gackt was working as a host and dealer in a casino, while also being an assistant drummer for an amateur band. At the time he wanted to become more serious about his music activity but had a negative perspective on life. While at the casino, he met a businessman who inspired him to find a purpose in life, that being music. About a year later he left the band and he found himself working multiple jobs, among them as a sound technician at a studio where he could practice drums. When Gackt was twenty-years old, he met guitarist You Kurosaki, his future solo career support guitarist, at a music live house in Kyoto. They formed the band, Cains:Feel, whose name had biblical reference to the story of Cain and Abel. The group lacked a vocalist, so Gackt became the frontman, and the band went to record a demo tape before disbanding.

In 1995, he was introduced to the visual kei band Malice Mizer which was on hiatus due to the departure of their frontman Tetsu. Gackt moved to Tokyo and joined them in October 1995. As their vocalist, pianist and primary lyricist on studio albums Voyage Sans Retour (1996) and Merveilles (1998), he also contributed three songs in their catalog, "Regret", "Hamon" and "Le Ciel", the latter being their most successful single as a band.

During this time, the band's fame soared; and, after four years and two studio albums, in January 1999, it was officially announced that he left the band. According to his interviews and autobiography, the issues with the management office, members' differences, and his isolation from the band led to his departure.