Teodoro A. Agoncillo (November 9, 1912 – January 14, 1985) was one of the pre-eminent Filipino historians of the 20th century. He and his contemporary Renato Constantino were among the first Filipino historians who earned renown for promoting a distinctly nationalist point of view of Filipino history (nationalist historiography). He was also an essayist and a poet.
Born in Lemery Batangas, Agoncillio obtained a bachelor's degree in philosophy from the University of the Philippines in 1934 and a master's degree in the arts from the same university the following year. He earned his living as a linguistic assistant at the Institute of National Language and as an instructor at the Far Eastern University and the Manuel L. Quezon University. In 1956, he published his seminal work, Revolt of the Masses: The Story of Bonifacio and the Katipunan, a history of the 1896 Katipunan-led revolt against Spanish rule and its leader, Andres Bonifacio. He garnered acclaim for this book, as well as criticisms from more conservative historians discomforted by the work's nationalist, perhaps even Marxist bent.