(CNN) -- Win Tin, a founding member of Myanmar's National League for Democracy who was jailed for 19 years for political activism, has died at Yangon Hospital. He was 85.
A National League for Democracy (NLD) spokesperson told CNN Win Tin was admitted to Yangon Hospital three weeks ago with a kidney problem.
One of Myanmar's most prominent dissidents, Win Tin was a journalist and writer who joined with Aung San Suu Kyi during her campaign in 1988, according to Nyan Win, the current spokesperson for the NLD.
He was arrested in 1989 by Myanmar's military rulers, who feared the strength of the pro-democracy movement.
"Immediately after his arrest, U Win Tin was kept without food and sleep for three days," Suu Kyi wrote about his imprisonment. "It appeared that the interrogators wished to force him to admit he was my adviser on political tactics, in other words, that he was my puppet master."
"A man of courage and integrity, U Win Tin would not be intimidated into making false confessions," she added.
Win Tin continued to push for democracy even while in prison, penning a letter to the United Nations that resulted in additional jail time.
Despite his key role as a political leader, Win Tin's personal life was largely solitary.
After he was released in 2008, he told CNN that he was a "vagabond" with no family or children because he had given his life to the fight for democracy in Myanmar.
While he struck an optimistic note about the progress that had been made in his country after his release, he noted there was still a "tremendous amount of work to be done."
"He was a great pillar of strength," said Nyan Win. "His demise at this important political juncture of transition is a great loss not only to the NLD but also to the country. We are deeply saddened."