Gunnar Johansen (January 21, 1906 – May 25, 1991) was a Danish-born pianist and composer. He was one of the chief proponents of the music of Ferruccio Busoni, whose mature keyboard works he recorded in their entirety, as well as the complete keyboard works of Johann Sebastian Bach. He was an important supporter of Harry Partch. In 1949, after hearing a performance of Partch's “U. S. Highball (A Musical Account of a Transcontinental Hobo Trip)”, he offered the struggling and recently homeless composer housing and a workspace in an abandoned blacksmith's workshop on his ranch in Gualala, California.

Johansen was also a scholar, educator and humanist. His many humanitarian efforts included establishment of the Leonardo Academy, dedicated to the integration of the arts and sciences.

Born in Copenhagen, Johansen was introduced to the keyboard by his father and made his hometown debut at the age of twelve. Remaining in his native Denmark, he went on to study with the pianist and conductor Victor Schiøler. At the age of fourteen, he moved to Berlin to further his musical education with Egon Petri, a disciple of Ferruccio Busoni. He also worked with Edwin Fischer and Franz Liszt's pupil, Frederic Lamond. He toured as a pianist in Europe in the 1920s and came to the United States in 1929, first settling in California, where he did weekly radio performances for NBC Radio Network in San Francisco.

In the 1930's, he began touring with what he called the Historical Series, a dozen concerts that traced the history of keyboard music. In one notable series, he traced the evolution of Liszt's Hungarian Rhapsodies from their earliest versions to their finished form. After he played the series at the University of Wisconsin in 1937, he was invited to become the school's artist in residence, the first musical artist in residence at an American university.

In the early 1940s, Johansen settled in Blue Mounds, Wisconsin, a small rural town approximately 25 miles west of Madison. It was here that many of his composing and recording projects took place.

At the University of Wisconsin in Madison, he taught, performed and broadcast concerts for 37 years, from 1939 to 1976. From the 1940s through the 1960s, his violin partner for performances and chamber music classes at the University was the renowned violinist, Rudolf Kolisch, leader of the Pro Arte Quartet and founder of the Kolisch Quartet which specialized in works by Schoenberg and the Second Viennese School and in 1927 and 1938 premiered two quartets by Schoenberg and Alban Berg's Lyric Suite and String Quartet.

Johansen died of liver cancer in 1991 at the age of 85 at his home in Blue Mounds.

In the 1950's, he shifted the focus of his performing activity from radio concerts to recording. He established his own label, Artist Direct, and was one of the first pianists to attempt to record all of Liszt's known piano music, researching and uncovering many previously unknown works during the 1960s. His recorded output of Liszt which, according to him he "never intended to be absolutely complete," totals 51 LP records. In addition, he produced 43 albums of Bach and seven recordings each of the piano music of Ferruccio Busoni and Ignaz Friedman.