Gary George Peacock (May 12, 1935 – September 4, 2020) was an American jazz double bassist. He recorded a dozen albums under his own name, and also performed and recorded with major jazz figures such as avant garde saxophonist Albert Ayler, pianists Bill Evans, Paul Bley and Marilyn Crispell, and as a part of Keith Jarrett’s “Standards Trio” with drummer Jack DeJohnette. The trio existed for over thirty years, and recorded over twenty albums together. DeJohnette once stated that he admired Peacock's "sound, choice of notes, and, above all, the buoyancy of his playing." Marilyn Crispell called Peacock a "sensitive musician with a great harmonic sense."

Peacock was born in Burley, Idaho, on May 12, 1935; his father worked as a business consultant for grocery stores, and his mother was a homemaker. He grew up in Yakima, Washington, where he attended Yakima Senior High School, now called A.C. Davis High School. His earliest musical experiences involved playing piano, trumpet, and drums. When he was 15, he heard live jazz for the first time, attending a Jazz at the Philharmonic concert featuring Oscar Peterson and Ray Brown. Peacock graduated in 1953; while playing for his class, he had a profound experience, stating: "I was playing the drums, and had the experience of being played rather than playing... I realized that something transformative had happened... and there was this certainty. From the bottom of my feet to the top of my head, it was totally clear: 'Oh, this is the direction to go.'"

After graduating, Peacock attended the Westlake School of Music in Los Angeles but was then drafted into the Army. While stationed in Germany, he played piano in a jazz trio, but switched to bass when the group's bassist quit. Peacock recalled: "The bass player got married, and his wife didn’t want him out any more. The band’s drummer... said, 'You play bass.' I said, 'I don't want to play bass...' As it turned out, he found a pianist, and I started playing the bass." According to Peacock, he "just sort of figured it out": "I seemed to progress pretty rapidly in a very short time. And since I was stationed in Germany and there weren't any bass players anywhere, it allowed me to be available to play sessions with different people in Frankfurt and the surrounding areas." He also recalled: "The instrument felt natural. It just turned out to be a recognition, like, 'Oh, this is it. This is good.'"

After being discharged from the Army in 1956, Peacock remained in Germany, playing with Hans Koller, Tony Scott, Bud Shank, Attila Zoller, and others, before returning to Los Angeles. He recalled: "I had a standing invitation for a scholarship at Westlake College of Music. So I went to the school. They said, 'Great. Unfortunately, the school is closing.' So I had to start looking for gigs right away. That ended my scholarly education." His bass playing at the time was influenced by Paul Chambers, Ray Brown, and Scott LaFaro, whom he befriended. He soon established himself as a bass player, participating in sessions with Barney Kessel and Art Pepper, and, in 1962, recording with Don Ellis (Essence), Clare Fischer (First Time Out and Surging Ahead), and Prince Lasha (The Cry!). He also married fellow musician Annette Peacock (they later divorced) and began a musical association with pianist Paul Bley, with whom he would go on to record nine albums.

While in California, Peacock heard the music of Ornette Coleman. Initially dismissive, he soon changed his mind: "It challenged that fixed position I had about what jazz improvisation should be and what the rules are. It created a pivot for me to embrace a much larger musical universe." Peacock reflected on how his thinking began to change:

I can remember when I was in Los Angeles about 1959 and I noticed that I was playing less time... In fact, playing the time became very irritating, it just felt like a straightjacket and I wanted to kind of break through that. I simply started listening in myself to what a bass could do and I just began to intentionally play out of time, with some notions, some glimmers of what could be done. I noticed that the time could literally be there and I could be playing something that was basically ametric and yet it worked in some way as far as my ears were concerned... An interesting question [came up]: What would happen if we didn't play the time but just allowed it to be there. Instead of going, 'dingdingding,' just allow it to be there and play something... It opened up something for the pianist, it opened up something for the drums.

In 1962, Peacock moved to New York, where he played with Bley and musicians such as Jimmy Giuffre, Roland Kirk, George Russell, and Archie Shepp. He also joined Bill Evans' trio, which included drummer Paul Motian, who would become a long-time associate, recording the album Trio 64 with the group in December 1963. Peacock recalled that Evans' "sense of harmony was exquisite... The harmonies, and the way that he would voice the harmonies, made a melody not only believable but [so] you wanted to fall in love with it. And because he played low, whatever the bass played, it could be heard; be an integral part of the music." In 1964, Peacock briefly joined Miles Davis' quintet, substituting for Ron Carter in April and May of that year. Reflecting on his time with Davis, he stated:

Miles probably said one of the most brilliant, useful, and necessary comments I've ever heard. Somebody was recording with him, and Miles looked at him and said, "What I want to hear is what you don't know." That is really the key: not playing what you know, playing what you don't know. To do that, you have to get very quiet inside, listen, and surrender to whatever that particular musical setting is. So it doesn't make any difference whether I'm playing standards or free stuff, because you're giving up any kind of fixed positions or attitudes you may have about what it should or shouldn't be. And to do that, you have to be vulnerable, to be in a place where you realize that what you're after, you cannot know. It's not conceivable. But it's there. It's the muse. So it's kind of a switch from the self playing the muse to the muse playing the self.