Answer by taking a quote from the following article:

Keith Jarrett (born May 8, 1945) is an American jazz and classical music pianist. Jarrett started his career with Art Blakey, moving on to play with Charles Lloyd and Miles Davis. Since the early 1970s he has enjoyed a great deal of success as a group leader and a solo performer in jazz, jazz fusion, and classical music. His improvisations draw from the traditions of jazz and other genres, especially Western classical music, gospel, blues, and ethnic folk music.

In 1983, at the suggestion of ECM head Manfred Eicher, Jarrett asked bassist Gary Peacock and drummer Jack DeJohnette, with whom he had worked on Peacock's 1977 album Tales of Another, to record an album of jazz standards, simply titled Standards, Volume 1. Two more albums, Standards, Volume 2 and Changes, both recorded at the same session, followed soon after. The success of these albums and the group's ensuing tour, which came as traditional acoustic post-bop was enjoying an upswing in the early 1980s, led to this new standards trio becoming one of the premier working groups in jazz, and certainly one of the most enduring, continuing to record and tour for more than 25 years. The trio has recorded numerous live and studio albums consisting primarily of jazz repertory material. The Jarrett-Peacock-DeJohnette trio also produced recordings that consist largely of challenging original material, including 1987's Changeless. Several of the standards albums contain an original track or two, some attributed to Jarrett, but most are group improvisations. The live recordings Inside Out and Always Let Me Go (released in 2001 and 2002 respectively) marked a renewed interest by the trio in wholly improvised free jazz. By this point in their history, the musical communication among these three men had become nothing short of telepathic, and their group improvisations frequently take on a complexity that sounds almost composed. The standards trio undertakes frequent world tours of recital halls (the only venues in which Jarrett, a notorious stickler for acoustics, will play) and is one of the few truly successful jazz groups to play both straight-ahead (as opposed to smooth) and free jazz. A related recording, At the Deer Head Inn (1992), is a live album of standards recorded with Paul Motian replacing DeJohnette, at the venue in Delaware Water Gap, Pennsylvania, 40 miles from Jarrett's hometown, where he had his first job as a jazz pianist. It was the first time Jarrett and Motian had played together since the demise of the American quartet sixteen years earlier.

what changeless successful?
Several of the standards albums contain an original track or two, some attributed to Jarrett, but most are group improvisations.