Isabelo de los Reyes Sr. y Florentino, also known as Don Belong, was a prominent Filipino patriot, politician, writer, journalist, and labor activist in the 19th and 20th centuries. He was the original founder and proclaimer of the Iglesia Filipina Independiente, the first-ever Filipino independent Christian Church in history in the form of a nationalist church, which was proclaimed in 1902. He is popularly known today as the "Father of Philippine Folklore", the "Father of the Philippine Labor Movement", and the "Father of Filipino Socialism".

The Philippine Independent Church is an independent Christian denomination, in the form of a nationalist church, in the Philippines. Its schism from the Roman Catholic Church was proclaimed during the American colonial period in 1902, following the end of the Philippine–American War, by members of the Unión Obrera Democrática Filipina due to the pronounced mistreatment towards the Filipinos by Spanish priests, and partly influenced by the unjust executions of José Rizal and Filipino priests and prominent secularization movement figures Mariano Gomez, José Burgos, and Jacinto Zamora, during earlier Spanish colonial rule wherein Roman Catholicism was the state religion in the country at the time.