Beginning in the early 1950s, Mr. Leonhardt became known for his interpretations of the music of Johann Sebastian Bach and other composers of the 17th and 18th centuries. Through painstaking historical scholarship, in which he pored over musical manuscripts in European archives, Mr. Leonhardt arrived at a new style of performance that was radical in its simplicity.
He sought, as much as possible, to play the music in precisely the manner that Bach, Girolamo Frescobaldi, Domenico Scarlatti and other early masters of the keyboard had done centuries before. Mr. Leonhardt insisted on using original instruments — or faithful reproductions — and helped bring the harpsichord back into the musical mainstream.
He made hundreds of recordings, including three separate versions of Bach’s “Goldberg Variations,” and his concert performances were eagerly awaited by aficionados around the world. Audiences would begin to applaud as soon as a stagehand came onstage to raise the lid of Mr. Leonhardt’s harpsichord.
In 1983, Washington Post reviewer Lon Tuck called Mr. Leonhardt the “grand guru of the Baroque musical revival.”
“As harpsichordist, organist, conductor, musicologist and teacher,” Tuck continued, “he has influenced the new crop of Baroque musicians as much as any single person.”
Before Mr. Leonhardt and a few other stalwarts of the so-called “period music” movement began to insist on historical authenticity, Baroque and early classical music was often given haphazard treatment. Little consideration was given to instrumentation, dynamics or the size of an orchestra.
Mr. Leonhardt made his solo debut on harpsichord in 1950 and, two years later, published an important historical study of Bach’s music. His 1953 recording of Bach’s “The Art of Fugue” became a landmark in which all the historical puzzles of tempo and dynamics were solved.
Almost at once, interest in Bach and other pre-Romantic-era composers began to grow.
“It spread like wildfire,” Mr. Leonhardt told England’s Guardian newspaper in 1985. “Performing standards rose very quickly. ... The public has changed, too. The original handful of aficionados has turned into a vast and very knowledgeable audience.”
In time, however, some critics and musicians began to wonder if the early-music movement was taking itself too seriously.
When Mr. Leonhardt conducted choral or operatic music, he sought to use boy sopranos or high-voiced countertenors, in the 17th-century style. Instruments were tuned as much as a full pitch lower than modern ears are accustomed to. He was sometimes distressed that his concerts were illuminated by electric lights instead of oil lamps.
“Leonhardt is a very sober man whose sense of humor, if it exists, is not permitted to surface when he is in the midst of a performance,” critic John Kraglund wrote in the Toronto Globe and Mail in 1982.
Mr. Leonhardt disputed that he was living in the past. He continued to refine his musical interpretations throughout his life.
“I can’t stand pedants,” he said in 1985. “A musician should make sure his basic principles are right, then express himself according to his temperament.”
Gustav Maria Leonhardt born May 30, 1928, in ’s-Graveland, Netherlands, and was the son of a music-loving banker. The younger Leonhardt studied the piano and cello before discovering the harpsichord when he was 15.
During World War II, he went into hiding to avoid being forced to work in a factory in German-occupied Amsterdam. In the late 1940s and early 1950s, he studied and taught at conservatories in Basel, Switzerland, and Vienna.
By 1954, he had joined the faculty of the Amsterdam Conservatory and — like Bach — he was a longtime church organist. He lived for many years in a house built in 1605.
Survivors include his wife, violinist Marie Amsler Leonhardt; three daughters; and a sister.
In 1968, Mr. Leonhardt donned a periwig to portray Bach in a non-speaking role in “The Chronicle of Anna Magdalena Bach,” a German film that looks at Bach through the eyes of his second wife.
Besides his concerts and recordings, Mr. Leonhardt left a legacy as an influential teacher. In classes limited to five students, he taught some of the rising stars of a new generation of harpsichordists, including Christopher Hogwood and Ton Koopman.
“Unlike Bach,” he said, “I never had to teach little hooligans.”