Sam Bush was one of the key musicians who started the style of music called Newgrass. Using traditional bluegrass instruments, Newgrass has a slightly more modern sound than bluegrass, and involves more improvisation. And, while bluegrass songs are often all played in much the same way, Newgrass approaches each song individually and creates a unique arrangement separate from the other songs.
Sam Bush seems to think harmonically, and his solos often sound as if they had been written out ahead of time. You can't go to two jam sessions without hearing someone who's playing was influenced in some way by Sam Bush.
Sam now tours with "The Sam Bush Band", and is said to put on some of the best live shows around. You can learn more about him at his website.