Question: Who pioneered minimal music in the mid to late 1960s and performed in The Festival Dancing in Your Head? 
Context: Anthony Gatto (born in Brooklyn, New York), is an American composer of music for theater, dance, film, opera, and concert music.  He is also the founder of "The Festival Dancing in Your Head", held at the Walker Art Center, dedicated to the music, ideas, and influences of Ornette Coleman. Happy Family is Japanese instrumental progressive rock band based in Tokyo formed in 1987 with member in the musical circle of the University in Tokyo.  They influenced by music of Recommended Records type or Zeuhl (which is the music by French progressive rock band Magma), but they also have an influence of minimal music, and are focusing on extremely complex and dynamic rhythm which makes their music unique and original.  They stopped their musical activity since the end of 1990s for 15 years, but they restarted once again from early 2010s.  They are now active, releasing new album along with attending 1st edition of Rock in Opposition Japan Festival in 2014. Drone music, drone-based music, or simply drone, is a minimal music genre that emphasizes the use of sustained or repeated sounds, notes, or tone-clusters – called drones.  It is typically characterized by lengthy audio programs with relatively slight harmonic variations throughout each piece.  La Monte Young, one of its 1960s originators, defined it in 2000 as "the sustained tone branch of minimalism". Maximalist!  was an ensemble formed to perform the compositions that Thierry De Mey and Peter Vermeersch wrote for the dance choreographies of Wim Vandekeybus.  The music they performed mixed avant-garde jazz with minimal music; hence (by contrast) the name of the band. Progressive rock is a radio station programming format that emerged in the late 1960s, in which disc jockeys are given wide latitude in what they may play, similar to the freeform format but with the proviso that some kind of rock music is almost always played.  It enjoyed the height of its popularity in the late 1960s and 1970s.  The name for the format began being used circa 1968, when serious disc jockeys were playing "progressive 'music for the head'" and discussing social issues in between records.  During the late 1960s, as Long playing records began to supplant the single in popularity with rock audiences, progressive rock stations placed more emphasis on album tracks than their AM counterparts. <ref name="Prog. radio/albums"> </ref> Throughout the 1970s as FM stations moved to more structured formats, progressive radio evolved into Album-oriented rock (AOR). Stephen Michael Reich ( or ; born October 3, 1936) is an American composer who, along with La Monte Young, Terry Riley, and Philip Glass, pioneered minimal music in the mid to late 1960s. Vula Viel is a jazz group from London, playing music based on the sound of the gyil, a wooden xylophone from West Africa, fused with elements of electronica and minimal music.  The group was formed by Bex Burch, a musician from Yorkshire.  Burch trained in percussion at the Guildhall School of Music and Drama, where she was introduced to the minimalist music of Steve Reich, and then spent three years with the Dagaaba people of the Upper West Region of Ghana.  There she learned music and xylophone making as the apprentice of a master xylophonist, before returning to the United Kingdom and forming Vula Viel.  The name "Vula Viel " was given to Burch on the completion of her apprenticeship, and means "Good is Good" in the Dagaaba language, Dagaare. Math rock is a style of indie rock that emerged in the late 1980s in the United States, influenced by post-hardcore, progressive rock bands such as King Crimson and 20th century minimal music composers such as Steve Reich.  Math rock is characterized by complex, atypical rhythmic structures (including irregular stopping and starting), counterpoint, odd time signatures, angular melodies, and extended, often dissonant, chords.  It bears similarities to post-rock. The Festival Dancing in Your Head is a festival dedicated to commissioning, producing, and presenting new music and music films from around the world.  The festival is produced by Headwaters Music, a non-profit music organization, led by composer Anthony Gatto.  The 2005 festival at the Walker Art Center in Minneapolis celebrated the 75th birthday of Ornette Coleman with nearly 100 international musicians, including an evening with The Ornette Coleman Quartet.  Past festival performers include the Kronos Quartet, Bang on a Can All-stars, So Percussion, Alarm Will Sound, Iva Bittová, Ethel, Flux Quartet, The Bad Plus, Happy Apple, Low, Gao Hong, Dean Granros and Antigravity, Tibetan Monks of the Gyuto Wheel of Dharma Monastery, Dosh, Patrick Crossland, Douglas Ewart, Anthony Cox.  Composers performed include Steve Reich, David Lang, Michael Gordon, John Adams, Arvo Pärt, György Ligeti, Martin Bresnick, Brian Ferneyhough, Annie Gosfield, John King, Phil Kline, Evan Ziporyn, Béla Bartók. Minimal music is a form of art music that employs limited or minimal musical materials.  In the Western art music tradition the American composers La Monte Young, Terry Riley, Steve Reich, and Philip Glass are credited with being among the first to develop compositional techniques that exploit a minimal approach.  It originated in the New York Downtown scene of the 1960s and was initially viewed as a form of experimental music called the "New York Hypnotic School."  As an aesthetic, it is marked by a non-narrative, non-teleological, and non-representational conception of a work in progress, and represents a new approach to the activity of listening to music by focusing on the internal processes of the music, which lack goals or motion toward those goals.  Prominent features of the technique include consonant harmony, steady pulse (if not immobile drones), stasis or gradual transformation, and often reiteration of musical phrases or smaller units such as figures, motifs, and cells.  It may include features such as additive process and phase shifting which leads to what has been termed phase music.  Minimal compositions that rely heavily on process techniques that follow strict rules are usually described using the term process music.
Answer: Steve Reich