Tony Nicklinson, a man with locked-in syndrome who fought for the right to legally end his life, has died.
The 58-year-old was paralysed from the neck down after suffering a stroke in 2005 and described his life as a "living nightmare".
Last week Mr Nicklinson, from Melksham, Wiltshire, lost his High Court case to allow doctors to end his life.
Mr Nicklinson's family solicitor said that he had refused food from last week.
Lawyers for another man, 47, who lost his High Court case alongside Mr Nickinson, are to appeal against the decision.
They said it denied their client "the opportunity to take the necessary steps to end his own life".
Mr Nicklinson's family solicitor Saimo Chahal said he died at home at about 10:00 BST in the presence of his wife, Jane, and two daughters, Lauren and Beth.
She said: "Jane told me that Tony went rapidly downhill over last weekend, having contracted pneumonia."
'Heartbroken by decision'
She added: "Jane said that, after Tony received the draft judgment on 12 August refusing his claim, the fight seemed to go out of him.
"He said that he was heartbroken by the High Court decision that he could not end his life at a time of his choosing with the help of a new doctor.
"He could not understand how the legal argument on his behalf could not succeed."
She said Mr Nicklinson had told her two days after the ruling he was "crestfallen, totally devastated and very frightened".
He had added: "I fear for the future and the misery it is bound to bring.
"I suppose it was wrong of me to invest so much hope and expectation into the judgment but I really believed in the veracity of the argument and quite simply could not understand how anybody could disagree with the logic.
"I guess I forgot the emotional component."
Ms Chahal said Mr Nicklinson had made an advanced directive in 2004 refusing any life-sustaining treatment.
His family had earlier updated his personal Twitter account.
The messages said: "You may already know, my Dad died peacefully this morning of natural causes. he was 58.
"Before he died, he asked us to tweet: 'Goodbye world the time has come, I had some fun'."
Gezz Higgins, a friend and former rugby club team-mate in Kent, said before his stroke he was a "happy-go-lucky" man.
"He was an exceptionally good and sociable guy," he said. "The sort of fella who, when he walked into a room, you knew things would liven up a bit."
Wiltshire Police said the force was not investigating Mr Nicklinson's death.
Mr Nicklinson had been paralysed since suffering a stroke while on a business trip to Athens.
He had campaigned for the law to be changed to allow doctors to assist his suicide without fear of prosecution.
Prior to last week's case, in an article he wrote for the BBC, he had described his life as "a living nightmare".
He said: "What I find impossible to live with is the knowledge that... I have no way out - suicide - when this life gets too much to bear."
He added: "It cannot be acceptable in 21st Century Britain that I am denied the right to take my own life just because I am physically handicapped."
However, three High Court judges rejected his plea for the law to be changed, saying the issue should be left to Parliament.
Mr Nicklinson said he would appeal against the decision but his lawyer said this would not end unless "someone steps forward in similar circumstances to pursue the action".
Professor Penney Lewis, professor of law at the Centre of Medical Law and Ethics at King's College London, said that Mr Nicklinson's plight would continue to raise questions about a change in the law.