Second World War veteran and political commentator Harry Leslie Smith has died aged 95.
Mr Smith, from Barnsley in South Yorkshire, championed human rights and the welfare state, and appeared at the Labour Party conference in 2014 to speak about life before the NHS.
A post on his Twitter account, which has more than 250,000 followers, announced his death on Wednesday morning.
The tweet said: "At 3:39 this morning, my dad Harry Leslie Smith died. I am an orphan. #istandwithharry".
The verified Twitter account links to a Facebook page called Harry's Last Stand.
A post on that page, dated November 21, says: "My dad, Harry Leslie Smith is critically ill in hospital in Ontario Canada after a fall, yesterday morning. You can follow updates on his twitter feed @harryslaststand and the hash tag #IStandwithHarry This is his son, John."
Former Labour leader Ed Miliband tweeted: "Very sad to hear of the death of Harry Leslie Smith. He was one of a kind who never wavered in his fight for equality and justice. We should all carry his passion, optimism and spirit forward."
Labour MP Jonathan Ashworth wrote on Twitter: "RIP Harry Leslie Smith will always remember this wonderful speech on the NHS you gave at Labour Conference."
Labour MP Luke Pollard also paid tribute, tweeting: "RIP @Harryslaststand. Harry Leslie Smith came to #plymouth ahead of the 2015 General Election. He was old and frail but full of life. His encouragement and positivity was a true inspiration. RIP Harry"
Mr Smith, an RAF veteran, survived the Great Depression and Second World War, and rose to prominence in 2013 after writing an article for the Guardian declaring that he would no longer wear a poppy.