Lou Reed, one of the most influential songwriters and guitarists of the past 50 years, died Sunday. He was 71. The cause of death is unknown, although he underwent a liver transplant in May. Reed befriended musician John Cale in the mid ‘60s, and later formed the Velvet Underground with Sterling Morrison and Maureen Tucker. They caught the attention of Andy Warhol, who incorporated the Velvets into his Exploding Plastics Inevitable. Cale wrote of Reed's passing: "The news I feared the most, pales in comparison to the lump in my throat and the hollow in my stomach ... No replacement value, no digital or virtual fill...broken now, for all time. Unlike so many with similar stories - we have the best of our fury laid out on vinyl, for the world to catch a glimpse. The laughs we shared just a few weeks ago, will forever remind me of all that was good between us."