String bending separates the guitar from most other polyphonic instruments. The ability to manipulate the pitch of a note by a value less than a semitone, add vibrato akin to that of a vocalist, and bend notes in an emotive manner is something that gives guitarists their unique voice.
Many players spring to mind when we think about string bending; the soulfulness of David Gilmour, the emotive touch of Eric Clapton, the modern manipulation of Steve Vai, and the wild style of the late Dimebag Darrell are all examples of how string bends can separate one