Only five? Well.......
1. Andres Segovia. While surpassed in technique by many of his students, Segovia was the first to create guitar transcriptions of large potions of the classical canon. In this way, the entire modern idea of "classical guitar" rests on his shoulders.
2. Django. His phrasing is still heard in every jazz player and in many rock players as well.
3. Charlie Christian. The first plugged-in player, he moved the guitar from the rhythm section to center stage, defining the tone of jazz guitar guitar in the process.
4. Don Rich. As the lead picker in Buck Owen's Buckaroos, he laid the foundation of the modern country lead player, Telecaster twang and all. Again, he was surpassed in technique many times over, but there's no Albert Lee without Don.
5. Jim Hendrix. Every long, legato, high gain line ever played in rock music owes a debt to Jimi. He cranked the blues until it became rock guitar: his legacy remains inescapable even now.