Takeshi Itoh (伊東たけし; real name 伊東毅, also spelled Takeshi Ito or Takeshi Itō, and known to fans as T.K.) is the saxophonist, flutist and wind-synthesizer player whose horn has carried the sound of T-Square through most of the band's history. He was born in Fukuoka on March 15, 1954, and started on piano and violin as a child. In junior high he played euphonium and tuba in the brass band, took up flute at Seinan Gakuin High School, and then moved to alto saxophone after reading the autobiography of Sadao Watanabe. He studied at the College of Art at Nihon University in Tokyo, where he played in the Rhythm Society Orchestra and in the bands Witch Hunt and Last Day.

When Witch Hunt broke up in 1977 he joined The Square, the Tokyo fusion band that would later be renamed T-Square. Discogs credits him on the group's first records of 1978, Lucky Summer Lady and Midnight Lover. Outside the band he was already a working horn player in the Tokyo fusion scene. He is credited on tenor saxophone with Naoya Matsuoka on Day Break (Naoya Matsuoka & His All Stars, Union Records, 1979), on tenor saxophone and flute on Matsuoka's The Wind Whispers (Wesing, Warner Bros., 1979), on flute on Son (1980), on flute and alto saxophone as a guest on The Show (1981), and on tenor saxophone and flute on The September Wind (1982). In 1980 he played alto saxophone on George Kawaguchi's African Hot Dance, credited to George Kawaguchi and Super Fusion Band.

The 1980s are the decade in which his tone became the band's calling card. He played the Lyricon, an early wind synthesizer, alongside the saxophone, and Discogs credits him on both instruments on Truth (1987), the album that gave T-Square the theme Japanese television used for its Formula One coverage. In 1984, when two tracks from Adventures were used in Suntory White television commercials, he appeared in the advertisements. That same year, on September 21, CBS/Sony released his first record as a leader, Dear Hearts, followed by El Seven in 1985, made with the New York keyboardist Philippe Saisse and the guitarist Randy Fredrix. T.K. (1988) took its title from his nickname and was produced in part by David Frank and Mic Murphy of The System; its lead track, "Cowbell", also came out as a US Columbia 12 inch the same year. The 1984 Brues for Lee 12 inch single, which pairs two tracks from Dear Hearts, credits on Discogs a rhythm section that includes Nathan East on bass, John Robinson on drums, Paul Jackson Jr. and Dann Huff on guitars and Paulinho Da Costa on percussion, with a horn section arranged by Jerry Hey.

At the end of 1990 he left T-Square to concentrate on a solo career, and Natural (1990) was the last album of his first stretch with the band. Masato Honda took over the saxophone chair in 1991. The records that followed were made for Atlantic and then EastWest. Visions (1992) was produced by Saisse. T.K. LA (1993) was produced by the drummer Ricky Lawson in Los Angeles, with Paulinho Da Costa, Greg Phillinganes, Neil Larsen, Paul Jackson Jr., the Earth Wind & Fire Horns and Norihito Sumitomo on EWI. Groove Island (1994) added the New West Horn, a four-piece section that included the saxophonist Andy Snitzer and the trumpeter Chris Botti. T.K. Covers (1995) gave pop and rock standards such as "September" and "Dust in the Wind" a saxophone treatment, T.K. Breeze (1996) was produced by his T-Square bandmate Masahiro Andoh, and Scare Headline (1997), which he co-produced with Sumitomo, closed the Atlantic and EastWest run. Love (1997) turned to songs by the Beatles and John Lennon. In the same years he played alto saxophone on Jimsaku's Wind Loves Us (1993) and Blaze of Passion (1995), and he had already added saxophone to Tetsuo Sakurai's Dewdrops in 1986. He also guested on Hiroshima's East (1989) and appears on the soundtrack albums for two Detective Conan films.

Near the end of the decade he moved toward club music. Double Circle (1999) and Turn Over (2000) were released by Kitty Records with Taku Nakamura and Makoto Kuriya, and Discogs files them under acid jazz and future jazz. In late 2000 he returned to T-Square, starting with Friendship (2000), on which Discogs lists him on alto saxophone, flute and EWI. He has remained with the band since. Mellow Madness (Village Records, 2007) is a collection of soul and jazz standards, and in 2014 he released Favorites, his first solo album in seven years.

Since then he has led his own Mellow Madness Septet at Cotton Club Japan in Tokyo, with dates on February 19 and 20, 2022, followed by Luxury Night 2023. When Masahiro Andoh left T-Square on February 1, 2021, Itoh became in effect the band's leader. He and the drummer Satoshi Bandoh carried it forward, and he is credited as a producer on Wish (2022). The most recent T-Square album, Voyage, came out in 2026. He has also continued to play on other artists' records, among them the vocalist Yasuko Agawa's Light Mellow Deluxe (2025). Since 2023 he has used the NuRAD wind controller, and in 2025 a NuRAD R2 signature model carrying his name was released. He turned 72 in March 2026.

Itoh's route into jazz ran through Sadao Watanabe, whose autobiography moved him from flute to alto saxophone, and through the college big-band tradition at Nihon University. His playing lives where Japanese jazz-fusion meets pop melody: clear phrasing, a bright alto tone and long, singing lines that suit the themes T-Square is known for. He is first of all a melodist, and the band's biggest hit became a household sound in Japan through television.

His solo records show a different range from the band's. The 1984 to 1988 albums sit in the Los Angeles and New York studio-fusion lineage, with American producers and rhythm players. The Atlantic and EastWest albums of the 1990s lean toward jazz-funk and contemporary jazz, and T.K. Covers and Love reinterpret pop and rock songs. Double Circle and Turn Over reach for acid jazz and future jazz, while Mellow Madness returns to soul and jazz standards.

He has also been an early adopter of electronic wind instruments, moving from the Lyricon in the 1980s to the Akai EWI and, in recent years, the NuRAD controller.

In the Japanese scene, T-Square and its peers such as Casiopea are treated as jazz-fusion bands, and Discogs files most of Itoh's own releases under Jazz. The music is instrumental and accessible rather than improvisation-driven, so his work is better described as fusion and smooth jazz than as straight-ahead playing.