He also fought for the right of gay high-school students in Salt Lake City to organize a club, and argued against discrimination in the Boy Scoutss of America and the military.
Buckle's immolation was part of an environmental protest.
"Pollution ravages our planet, oozing inhabitability via air, soil, water and weather", Buckel continued. A suicide note read that Buckel used a "fossil fuel" to commit the suicide, indicating the action was done as a type of ecological protest.
"The news of David's death is heartbreaking".
As a senior attorney with LGBT civil rights organization, Lambda Legal defense, Buckel was a lead lawyer in a 2000 lawsuit on behalf of transgender 'Boys Don't Cry' rape-murder victim Brandon Teena, helping the family recover additional damages from neglectful Nebraska law enforcement.
After his lengthy legal career, Mr Buckel became deeply involved in environmental causes.
He wrote a note before setting himself on fire on Saturday morning.
The two notes were found inside a garbage bag inside a shopping cart near his body. He also emailed the text to several local media outlets, including The New York Times.
Buckel on the left in 1999 besides James Dale, a man he was defending for being kicked out of the Boys Scouts when the leaders found out he was gay.
He said that privilege comes with the suffering of others.
Mr Buckel also insisted in the email he was in "good health to the final moment".
Officials say it was the former cause he referenced repeatedly in his letter, along with the Tibetan tradition of protest suicides similar to that reportedly causing his death.
Told Irena Ryjova, 44 who came past the 'mass" just after 7 am, an hour after Buckel burned himself, "It was just lying there, on its back, knees slightly bent like someone would lie on the sand at the beach'.
A jogger who stumbled across the remains and shared photographs of them on Twitter before they were covered up by police said they were "freaked out" by the discovery.
"His thoughtful and engaging advocacy broke through many stubborn misconceptions and showed it was possible and necessary for our movement to speak up for bullied, ostracised LGBT young people", she said in a statement to the Huffington Post. She called Buckel "one of the architects of the freedom to marry and marriage equality movement". Now, Sommer is the general counsel for the Mayor's Office of Criminal Justice.