Bluegrass is an outgrowth of country music. Originally conceived as a way to keep country pure as the genre's popularity continued to grow, it has developed into a style of its own, with its own traditions and quirks. If there is anyone responsible for bluegrass, it's Bill Monroe; the genre itself was named after his band. Monroe developed the genre's signature style -- hard, fast tempos; high, close harmonies; and a pronounced emphasis on instrumental technique -- in the mid-'40s, and he popularized it during the '50s. By the end of that decade, their sound had become part of country music, and there were legions of bands that followed in their footsteps. During the '60s, such groups as the Dillards took bluegrass further, adding rock and jazz influences to the music and creating the progressive bluegrass subgenre. Progressive bluegrass continued to grow over the next three decades, as traditional bluegrass adhered to the original ideals of bluegrass.