Prehistory of Gromov-hyperbolic spaces/groups When speaking about hyperbolic groups/spaces, one usually refers to Gromov's monograph Hyperbolic groups for their introduction. However, coarse notions of hyperbolicity can be found in some of his earlier texts, such that Infinite groups as geometric objects and Hyperbolic manifolds, groups and action. Also, among the (many) equivalent definitions of $\delta$-hyperbolic spaces, one of them refers to Rips' condition, suggesting that E. Rips played some role here.
Hence my question:

What is the prehistory of Gromov-hyperbolic spaces/groups?

Here, "prehistory" refers to "before Gromov's monograph".
Edit: I should specify that I am not looking for the historical motivations of the definition, but the origins of the definition itself. How did the definition emerge?
 A: Gromov, in his monograph (see page 83 of "Essays in group theory"), writes the following.

The idea of hyperbolicity has been lingering in combinatorial group theory since the basic work by Dehn. An extensive study of a class of word hyperbolic groups $\Gamma$ with $\mathrm{dim}\, \partial \Gamma = 1$ (in the combinatorial disguise) was conducted by Olshanski (see [Ol]). Deep algebraic results on general hyperbolic groups are contained in the as yet unpublished work by I. Rips who calls them
groups with negative curvature.

As you note, Gromov's earlier papers contain relevant work.  Gromov also refers to Cannon's work, but only as regards rationality of certain languages.  I believe that Cannon's treatment of quasi-geodesic stability, and its relevance for hyperbolic groups, slightly predates Gromov's.
Both Cannon and Gromov are alive and both reply to email.  So perhaps it would be better to contact them directly.
A: The notion of coarse curvature was very popular in the "Leningrad math school" where Gromov is from before Gromov, for example, see the works of D. Alexandrov and Toponogov. The small cancelation idea which goes back to Dehn was very popular in other parts of the USSR, especially in Moscow (Grindlinger, Novikov, Adian, Olshanskii and others) but did not influence Gromov's work very much, although groups with thin geodesic triangles are studied already in the work by Novikov and Adian. So in some sense Alexandrov, Toponogov, Novikov and Adian predated Gromov.
