As we all know the guitar existed since ancient times, However the electric guitar was invented in 1935, using electro magnetics to pick up the vibrations of the strings and amplifying the sound via a amplifier.
But since the 30s, amplification meant guitar could be played in a new way, and a music genre was born thanks to amplification.
The 1950s and first ever rock recording
In 1958, Link wray a blues/rock n roll guitarist pierced holes in his amplifier speaker to get a fuzzy distorted tone...the result when he played and strummed barre chords he got this overdriven sound, A sound which became known as rock music, below is his record considered the first actual rock song.
The Invention of Overdrive and First Heavy metal song ever
1965, The beatles recorded helter skelter considered by many the first heavy metal song, The song featured the use of overdriven guitars and much more energy than previous mellow beatle records.
Amplification alone meant you could hammer on and make notes sound just by touching the fretboard, But thanks to overdrive, overtones and higher frequencies can be heard. So ever detail is heard.
By the mid 60s, many guitarists were already using overdrive effect pedals instead of the old trick of artificial overdrive by piercing the speaker.
Hendrix and The rock and blues connection
Blues a simple art was more geared towards the black audiences, after all it had it's roots in slavery times.
Where African American slaves played western guitars using western musical scales with unconventional chords like dominant sevenths, which is technically wrong musically and then mixing the western scales with natural African scales deriving a note from it,
The blues note often called in musical terms diabolus in musica or diminished fifth interval which was a note that sound off and too dissonant for most classical muscians was often quite used in blues music, dom7 chords have diminished fifth intervals in them and the blues scale with the blues note too.
Robert Johnson the first blues guitarist from the 1930s, is rumoured to had sold his soul to the devil in exchange for his guitar playing abilites.
Hence the connection.
Bearing in mind many early rock groups such as the beatles, rolling stones, and even hendrix himself were all inspired by earlier blues records.
Hendrix himself modelled himself to sound like albert king, A famous blues guitarist of the 60s.
Hendrix is even quoted saying he wanted to do what little richard does with his voice on the guitar.
first starting out as a session guitarist originally playing rythmn and blues backing soul singers, until he made his break in 65, below you can see hendrix in the backing band to the left, ignore the annoying dancers.
Hendrix and Whammy Bar, Wah Wah Pedal
Hendrix laid much of the groundwork for blues rock guitarists in the late 60s and 70s, His signature sound used effect pedals like the wah wah pedal, a effect that gave this unusual funky sound.
He favoured the use of the whammy bar and popularized it's use in rock music, his lead guitar playing defined the sound of rock guitarists and influenced many including jimmy page, tommy iommi.
First Downtuned Record
Black sabbath released Children of the grave in 19712, the first band to ever downtune and use Drop C# tuning, which is unusally low and deep tuning for guitar, whereas the normal tuning for guitar was e standard or even e flat which was common in the 70s.
First Tapping Record
Rock guitarist were looking to push the extremes and experiment, But also on in particular was Eddie van halen in the late 70s and early 80s and his band, Eddie van halen recorded eruption, on it the best guitar solo at the time and the first to use tapping.
Eddie van halen used a technique called "tapping", where the guitarist uses the fingers to sound notes instead of picking them intime with fast trills to achieve the tapping sound, he also used pinch harmonics or "squealies" to get a high pitched sound.
Joe Satriani, Ygwie Malmsteen and Kirk Hammett
Joe satriani was not really active in the 80s, but he taught metallica and Testament lead guitarists to play.
Ygwie Malmsteen had a bigger contribution to rock music though, especially lead guitarists in the metal genre.
Neo-classical metal the genre he played, using arpeggios and sweep picking a technique not unheard of but popularized as the standard for many modern rock and metal bands.
Having it's roots in jazz music, claims jazz guitarists like les paul in the 1950s started sweep picking, but it's up for debate.
Modern era and 8 string guitars and Experimentation
Now rock and metal guitarists are pushing the limits of electric 6 string guitar, With the favourism of downtuning guitars to low tunings with many bands.
Bands like Korn began using 7 strings in Drop B tunings in the 90s.
Meshuggah a band from sweden was one of the bands that started using 8 string guitars in 2003.
There achieved a low bassier guitar sound,
These days there's many rock guitarists looking to better the craft, John Petrucci, Lucas mann, Alex laiho, Muhammad Suicmez, Tosin Abasi, to name a few...