Writer Harry Smith stole the show in Labour's debate on health and social care, reducing some delegates to tears as he recounted life before the NHS.
Ahead of a speech by shadow health secretary Andy Burnham, Mr Smith said his childhood was a "barbarous time".
"Rampant poverty and no healthcare were the norm of the Britain of my youth."
In a speech greeted with a standing ovation and widely praised on Twitter, he warned that the UK must "be vigilant" about the NHS.
"I came into this world in the rough and ready year of 1923," Mr Smith said. "I'm from Barnsley, and I can tell you that my childhood, like so many others from that era, was not like an episode from Downton Abbey."
"Instead, it was a barbarous time, it was a bleak time, and it was an uncivilised time, because public health care didn't exist."
Hospitals, doctors and medicine were for "the privileged few, because they were run by profit", he said.
"My memories stretch back almost a hundred years, and if I close my eyes, I can smell the poverty that oozes from the dusty tenement streets of my boyhood," he added.
Mr Smith recalled the "anguished cries" of a woman dying from cancer who could not afford morphine, and how his eldest sister had wasted and died from tuberculosis at the age of ten, and was "dumped nameless into a pauper's pit".
His generation was "galvanised" after the Second World War to become "the tide that raised all boats", and his experiences led him to vote Labour and for the creation of the NHS in 1945.
"My heart is also with the people of the present, who because of welfare cuts and austerity measures are struggling once more to make ends meet, and whose futures I fear for," he added.
"Today, we must be vigilant, we must be vocal, we must demand that the NHS must always remain an institution for the people and by the people."
"We must never ever let the NHS free from our grasp, because if we do, your future will be my past."
Mr Smith's speech, which garnered two standing ovations and an acknowledgement from Mr Burnham, was hailed as a "masterclass" by Labour activist Paul Richards.
"Use of imagery, inversion, triclons, anecdotes, pathos, calls to arms: Harry Smith's address was a speech-writers' masterclass," Mr Richards tweeted.
Steve Hawkes, deputy political editor, of the Sun, tweeted: "91 year-old Harry Smith shows Ed Miliband how to do it - rousing speech (from autocue) that gets delegates on their feet."
The Conservative and Lib Dem coalition government has increased NHS spending each year during the current Parliament and both parties committed in 2010 to the founding values of the NHS that no-one, regardless of income, should be deprived of the best care.