After a more than year-long battle with pancreatic cancer, activist Pedro Zerolo died on Tuesday at the age of 55.
Colleagues have since started an online petition to change the name of Plaza Vázquez de Mella in Madrid to be named after Zerolo.
Prime Minister Mariano Rajoy was among the first to pay tribute, wrriting on Twitter: "We have just found out about the death of Pedro Zerolo. This is a very difficult moment for his family, his friends and his colleagues. My condolences."
Acabamos de conocer el fallecimiento de Pedro Zerolo. Un momento difícil para su familia, amigos y compañeros. Mi sentido pésame. MR— Mariano Rajoy Brey (@marianorajoy) June 9, 2015
Zerolo was born in Caracas, Venezuela in 1960 after his father was exiled by Spain's fascist dictator General Francisco Franco but he later moved to Spain to study law in Tenerife and then Madrid.
In the capital city, he started to become more involved in the LGBT community, working as a legal consultant for the Gay Collective of Madrid (COGAM) and later becoming the organization's president in 1993.
Eventually he was named president of what is now called the National Federation of Lesbians, Gays, Transsexuals and Bisexuals (FELGTB) and in 2004 joined the board of directors for the International Lesbian and Gay Association.
He also became elected to the Federal Executive Committee of the Spanish Socialist Workers' Party (PSOE) in 2004.
"If there was something that Pedro taught us, throughout the years that we were lucky to have him as our president and throughout all his work and commitment with FELGTB and PSOE, it is not to give up," wrote COGAM following the news of his death.
"You have to keep fighting and believe that change, as difficult as it may seem, is possible. The last months of his life were a new example of his determination to fight and to overcome."
Fighting for marriage equality
Starting in 2001, Zerolo began working on negotiations with government officials on amendments to the Spanish Civil Code regarding the definition of marriage.
Given his legal background, Zerolo worked on changing all mentions of "husband and wife" to "spouses", as well as "mother and father" to "parents".
In 2005, the Socialist administration of José Luis Rodríguez Zapatero passed laws allowing same-sex marriage as well as adoption rights for same-sex couples, making Spain the first country to grant full equality in marriage for both gay and straight couples.
That same year, Zerolo married his partner Jesús Santos.
After passing marriage equality, Zerolo worked on legislation to expand the rights of transgender individuals as well.
In the years since Zerolo's activism, Spain has now become known as one of the most progressive countries for gay rights in Europe, and has been previously ranked the most gay-friendly nation in the world.
Zerolo announced he had pancreatic cancer in January 2014, but he continued to stay in the public eye.
In his last interview with newspaper El Pais, he spoke openly about his feelings toward the sickness.
"I am ill, you know that," he said. "Illness has taught me that you reap what you sow. I have been surprised at all the sympathy I've been getting from strangers.
"I think that, in order to beat this, you cannot be afraid. Fear is defeated through calm, by being calm with yourself. Without fear, you feel that life is on your side."