'Guitar hero' is a term used (mostly by guitarists) for that certain type of player who has moved one step up from being just 'a guy who plays electric guitar' and has moved into the category of being 'the guy that hundreds want to play like'. A true guitar hero is a superman, a kind of 'minor deity' of guitarists. It's a term often used but rarely defined, partially because it's quite subjective, and one man's 'guitar hero' could (and probably would be) another man's 'emotionless shredder' or 'technically inept wailer'.
The concept of the 'guitar hero' is almost unique to guitarists. There are plenty of singers, drummers, violinists, cellists, flautists, etc who are all fantastic musicians, and who are held in great reverence by their fellow musicians, but there is a certain something about the electric guitar and its significance in popular music that has created this stereotype. The first real guitar hero was probably Jimi Hendrix, and it doesn't take an expert to work out why.
Guitar heroes are usually rock or blues guitarists. For example, Pat Metheny is one of the greatest jazz guitarists to ever live, but could not be described as a 'guitar hero' in the sense used by most guitarists. He may be many people's hero, and he is certainly a magnificent guitarist, but this is not enough to make him a 'guitar hero'. The main reason for this is that being a 'guitar hero' requires a certain amount of 'showmanship' and the image of being a 'rock star' more closely associated with rock and blues than styles like jazz or classical.
Though not ALL guitar heroes are particularly technically proficient, it is sort of a requirement by default. If they weren't technically proficient, other 'lesser' guitarists would have no real reason to 'worship' them. Exceptions to the rule are people like Kurt Cobain, whose chops weren't mind-blowing, but attained 'guitar hero' status through a generation of young guitarists who learned to play because of his music, and who all wanted to learn to play his material.
The crucial thing in the definition of 'guitar hero' is that it's more about being a 'hero' than it is about being a good 'guitarist'. This is why a guitarist like Adam Jones, the guitarist from Tool, is not a 'guitar hero' in the sense intended here. He's a rock guitarist, and he's a mind-blowing player, but he doesn't have the level of fame INDEPENDENT OF HIS BAND that would be required to be a 'guitar hero'.
As with all things, the line is blurred. While there are people who are definitely guitar heroes (Hendrix) and people who definitely aren't (Me) there are plenty who sit on the line. I like arguing about who is what. Try me.
Some examples of guitar heroes (in no particular order) include:
I'm sure I've missed PLENTY of absolute
rock-god guitar heroes, but it's not supposed to be a complete list, just a few
pertinent examples.
Anyone who really feels that a CRUICIAL guitar hero has been left out, feel free to /msg me.
Les Claypool of Primus is the only bass player I'm going to add to this list. Being a 'bass hero' is a completely different thing to being a 'guitar hero', but Claypool - even though he's a bass player - has so much of the 'mojo and swagger' associated with being a 'guitar hero' I think he deserves to be one anyway. I'm sure he would have something unpleasant to say about this, but that's just how it is. This proves even further that it's not so much about the playing as the attitude.