In 1966, Eric Clapton, Jack Bruce, and Ginger Baker came together to form a band that would change the face of rock and roll. Cream brought a heavier rock sound based around three absolute virtuosos at their instruments. Clapton is obviously Clapton, but Jack Bruce was a phenomenally gifted bass player who revolutionized the instrument in a rock context, and Baker was a beast on drums.
Their contributions to shaping the direction of rock in the latter half of the 60s cannot be overstated.
In addition to the hard rock oriented stuff, they were comfortable doing more experimental type rock as well
Probably not the most individually important rock band, but a profoundly important one nonetheless, and the average level of musicianship in the band has never been equaled.