Rock music has its origins in the 1920s with the "Tin Pan Alley" style of music. Originally the style of rock guitar was a fusion of pop, country, western and blues music. The popularity of Elvis Presley cemented the uptempo, backbeat-oriented style of his guitarist Scotty Moore into the definitive early rock guitar sound. Early rock pioneers such as Buddy Holly tended to favor a simple, austere style of guitar playing.
This changed in the next couple of decades, as rock musicians came to favor the electric guitar more and more. It rapidly became the primary type of guitar used in rock. Large amplifiers made rock guitar very loud. The guitar solo was a staple of rock music during the 1970s, so the rock guitar style began to center on the "hook."
From there, rock guitar to split into two styles: hard rock and punk rock. The hard rock and metal style became faster and more intricate, emphasizing heavy, aggressive and even discordant guitar playing. The punk rock guitar style appeared, harking back to rock guitar's early roots. Fast and simple, it eschewed the big hooks of the '70s.
Blues guitar originated in the Mississippi Delta around the turn of the 20th century, with a sparse, slow style that featured a 12-bar arrangement. Charley Patton and Robert Johnson are some of the founders of this style of blues guitar. When blues music traveled to Chicago in the 1920s, it changed. Muddy Waters, one of the first Chicago bluesmen, started using the electric guitar, and Chicago blues guitar became fast and highly energetic, a distinct style of its own, creating such legends as Willie Dixon and Howlin' Wolf.
Jazz guitar is one of the oldest styles of modern guitar playing. It has its roots in late-19th century brass band/ragtime styles and emphasizes improvisation and syncopation. One of its oldest and most definitive players was Blind Willie Dunn, who started performing in the 1920s. He was noted for changing chords on every beat, playing hard and soloing using only a single note. Django Reinhardt brought a gypsy influence to jazz guitar a short time later. The style went through a big change when Charlie Christian introduced the electric guitar to jazz music in 1936.
Bluegrass originated with a fusion of Delta blues and Appalachian folk music in the early 1900s. Guitar almost never functions as a lead instrument in bluegrass, but instead as a rhythm instrument. Early bluegrass guitar style was heavily influenced by banjo styles popular in folk music. The earliest bluegrass musicians, such as Charlie Monroe and Lester Flatt, used both a thumbpick for the bass runs and a fingerpick on the treble strings for rhythm. Though picks were not always used by bluegrass musicians, many bluegrass guitarists, such as Maybelle Carter, retained the technique of simultaneously using the bass and treble strings in this fashion.
Country and western were originally two different styles of music. Western originated in the American West in the early 20th century as a descendant of folk music and heavily influenced by swing. Western music tends to favor the steel guitar. Country music originated in the American Southeast in the late 1920s. Influenced by jazz and early rock, it also descended from folk music via bluegrass and favored a simple style of guitar playing akin to banjo. Western musicians such as Willie Nelson and country musicians like Chet Atkins made both genres so popular that their fusion in the 1960s created the country and western style.