Hercules's own article rightly gives pride of place to M13, the Great Globular Cluster whose stars are packed inside our own galaxy and which carried the 1974 Arecibo message toward it. A second cluster, much farther away and a different kind of object entirely, sits in the same figure and is easy to confuse with the first by name alone.
Abell 2151, the Hercules Cluster of galaxies, is a rich concentration of several hundred galaxies roughly 500 million light years away, far beyond anything in our own Milky Way, notable among galaxy clusters for the unusually large number of its members caught in the act of merging or interacting with one another rather than sitting apart as isolated systems. Where M13 is a ball of stars bound together by gravity within a single galaxy, Abell 2151 is an entire cluster of separate galaxies, each itself containing billions of stars, a difference of scale that the shared word "cluster" tends to hide rather than reveal.
The two objects have nothing to do with each other beyond sharing the constellation's outline as their address in the sky as seen from Earth, one a nearby star cluster suitable for a symbolic message to any possible listener, the other a distant laboratory for watching how galaxies collide and merge over time.
Hercules, known first simply as the Kneeler before it was fixed as the hero, holds one famous cluster and one considerably less famous one, at wildly different distances, both content to share his name.