NEW YORK — Lou Reed, the punk poet of rock 'n' roll who profoundly influenced generations of musicians as leader of the Velvet Underground and remained a vital solo performer for decades after, died Sunday at 71.

Reed died in Southampton, N.Y., of an ailment related to his recent liver transplant, according to his literary agent, Andrew Wylie, who added that Reed had been in frail health for months. Reed shared a home in Southampton with his wife and fellow musician, Laurie Anderson, whom he married in 2008.

Reed never approached the commercial success of such superstars as the Beatles and Bob Dylan, but no songwriter to emerge after Dylan so radically expanded the territory of rock lyrics. And no band did more than the Velvet Underground to open rock music to the avant-garde — to experimental theater, art, literature and film, to William Burroughs and Kurt Weill, to John Cage and Andy Warhol, Reed's early patron....