Dr Ian Davis was diagnosed with motor neurone disease (MND), also known as amyotrophic lateral sclerosis (ALS), in 2011.
In the seven years since then, he helped to raise tens of millions of dollars for research on the disease.
On Thursday, Davis died.
Davis, a doctor living in Melbourne, was diagnosed with the disease when he was 33.
MND gradually destroys nerve cells, affecting a person's ability to control the muscles you need to move, speak, eat and breathe. There is no cure, and patients live an average of two to three years after their diagnosis.
At the time of his diagnosis, Davis was working in haematology at Melbourne's Peter MacCallum Cancer Centre.
"Patients are diagnosed with MND at nearly the same rate as many other neurodegenerative diseases, but the fact stands: we don't live long enough to create a burden on society, so there is no incentive for governments or pharmaceutical companies to pursue new treatments," Davis wrote in an article about his disease in 2012. "There isn't enough profit to be made."
In 2014 Davis founded the Cure for MND Foundation and its Fight MND campaign, to help find a cure and effective treatments for MND.
Davis and his wife, Melissa, who is also a doctor, had a son, Archie, in 2014.
In September, Davis wrote on Facebook, "My fight is over," and said that he would soon remove his ventilator.
Hundreds of people wrote to thank him for the work he had done to find a cure for MND, and to tell him how he had inspired them.
They also wrote about his son Archie.
On Thursday, Davis posted a heartbreaking farewell message.
Davis thanked his followers for their support. "It has been some ride," he wrote. "I will leave this broken body with a full heart."
He asked that people that knew him write to his son via email to tell him what he was like.
"Please tell my boy I love him and I'm so proud to be his Dad," he wrote.
He also asked for people to donate to Fight MND.
Davis died a few hours later. He was 40.
Hannah Ryan is a reporter for BuzzFeed News and is based in Sydney.
Contact Hannah Ryan at email@example.com.
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