The guitar has been an integral part in a majority of popular music especially in the past 70-80 years. From Robert Johnson to Radiohead, the guitar covers almost every genre and style of music.
The traditional "hollow-body," or acoustic guitar has been around since the renaissance. However, with the creation of the electric guitar by legendary musician Les Paul (by attaching microphones to acoustic guitars) became a turning point in music. 1932 marked the first use of an electric guitar in a performance, and in 1946, Leo Fender patented his design for an electric guitar he called the "Esquire," or today's modern model, the "Telecaster!"
The guitar, for me, is iconic. It's the single most important element in Rock and Roll, but is versatile enough to accommodate a variety of sounds and styles.