Emilio Jacinto is historically known as the "Brains of the Katipunan" (Utak ng Katipunan). Joining the secret society at just 19 years old, he served as the chief advisor, chief strategist, and moral compass to founder Andrés Bonifacio. He shaped the ideological direction and moral code of the Philippine Revolution through several pivotal contributions:

The Kartilya ng Katipunan: Jacinto authored the society's primer. This document served as the ethical and moral guide for its members, emphasizing values like equality, honor, and love of country.

Kalayaan Newspaper: He edited and wrote for the Katipunan's official publication. Using the pen name Dimasilaw (while using Pingkian as his Katipunan alias), he published essays to spread principles of liberty and democracy.

Liwanag at Dilim: He wrote this masterpiece in prose—a compilation of essays tackling human rights, labor, government, and equality.

Military Leadership: Beyond his writings, Jacinto acted as a top-ranking military commander of the revolutionary forces. He eventually oversaw operations in Laguna until his untimely death from malaria at the age of 23.