Emilio Jacinto was only 20 when he joined the Katipunan. He was always thinking and prudent, but vehement and furious when he thinks he is right. This quality was admired by Bonifacio.

He wrote for the newspaper Kalayaan under the pen-name Dimasilaw, and was known in the Katipunan as Pingkian.

He was known as the brain of the Katipunan and the Revolution because he prepared and wrote many documents including the constitution, rules and the famous Kartilya ng Katipunan.