The King Cole Trio had no drummer. The time lived in the bass and in the pianist’s left hand, and the guitar answered the piano’s lines rather than strumming under them.

Three voices

With three instruments every line is heard. Oscar Moore’s guitar often played in unison with the piano’s right hand, or traded short phrases with it; the bass walked. When Cole sang, the piano did not stop: it filled the spaces between his phrases.

What it became

Wikipedia puts it plainly: the trio was the model for the small jazz groups that followed. Pianists from Oscar Peterson to Ahmad Jamal led trios of their own, some of them with exactly this line-up.

The photograph above: Oscar Moore with Nat Cole, July 1946, by William P. Gottlieb (public domain).