In a statement on Buckel's death, Lambda Legal described his death as "heartbreaking" and the attorney as a "beautiful human being".
Buckel, 60, who was also a green activist involved in various environmental causes, left a note explaining that the act of self-immolation was a protest against ecological destruction by fossil fuels.
In a suicide note emailed to the newspaper and several other media outlets, Buckel wrote that he had used fossil fuel to symbolize what was happening to the planet.
"Pollution ravages our planet, oozing inhabitability via air, soil, water and weather", he wrote in an email, according to the Times.
Buckel was marriage project director for Lambda Legal, and in that position he persuaded the organization to file a suit for marriage rights in Iowa in 2005, "at a time when only MA permitted same-sex couples to marry", noted a statement released by Camilla Taylor, the group's director of constitutional litigation and acting legal director.
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After citing the issues he hoped to bring attention to, reports indicate Buckel concluded with his hope that his would be "an honorable death that might serve others".
"My death by fossil-fuel reflects what we are now doing to ourselves".
The case was made famous in the 1999 movie "Boys Don't Cry", for which Hillary Swank won an Oscar for portraying Teena. Police said he was pronounced dead at about 6:30am.
He argued against the Boy Scout ban on gay, fought for the right of gay high school students in Salt Lake City to organize a club and helped a Pennsylvania woman win a lawsuit allowing her to put "beloved life partner" on the headstone of her partner. "Honorable goal in life invites honorable objective in death", he wrote.
Buckel's work included cases for Lambda Legal, the country's largest and oldest LGBTQ legal organisation. "He knew his craft and his trade and was strategic in how to build the blocks toward a sweeping victory".
Camilla Taylor, who is the current director of Lambda Legal, told the HuffPost that they will honor his life by "continuing to fight for equality".
"He deserves tremendous thanks for recognizing this was in many ways at the heart of what it meant to be gay for many Americans and making it a priority", said Susan Sommer, a former attorney for Lambda Legal "I learned so much from him about the emotional center of what it means for a gay person not to be able to have all the protections for the person they love and that it's worth fighting for", she added.