Born November 14, 1875 in Bulacan, Philippines. Gregorio del Pilar Sempio was one of the youngest generals in the Philippine revolutionary Forces. He was a general in the Philippine Revolution and Philippine-American war and was nick named boy General due to his youthful age. Gregorio was the youngest general to die during the wars.

Gregorio was the son to H. del Pilar and Felipa Sempio of Bulacan and nephew to Marcelo H. del Pilar a propagandist and Torbio H. del Pilar who exiled from Guam due to 1872 Cavite Mutiny involvement. Gregorio was also known as Goyo and he joined the insurgency when war broke out between the Philippine Revolution against the Spanish rule under Andres Bonifacio.

He enrolled at the Ateneo de Manila and lived with his uncle, Deodato Arellano. At the age of 20 years, he graduated from Ateneo de Manila University in 1896 where he received his Bachelors degree but the Revolution broke out thus he stopped studying. He and other young Bulakenos presented themselves for military service.

For his daring attacks in various encounters, he was steadily promoted in the military. Aguinaldo took notice of the young man. Gregorio was one of the signers of the Pact of Biak-na-Bato and he later joined Aguinaldo in exile in Hongkong. He became Aguinaldo's protege and confidential man.

On May 1898, upon resumption of hostilities against Spain, Aguinaldo designated him Dictator of the province of Bulacan and Nueva Ecija. On June 1, 1898, he landed at Kay Luntaw with rifles, established his headquarters at Matungao and started the seige of Bulacan. The Spanish troops signed the terms of surrender for the Spaniards while Gen. Gregorio del Pilar signed for the Filipino troops.

He continued his battles in Manila, Caloocan and Bulacan. He was sent to represent the military and the President in the two peace missions offering a ceasefire to the Americans after the fall of Malolos. He was made the Military Governor of Pangasinan and the right hand man of Gen. Aguinaldo. On November 22 he was ordered to defend and protect the Tirad Pass to cover the retreat of President Aguinaldo.

On the morning of December 2, 1899, Americans of the 33rd Infantry Volunteers under Major Payton C. March stormed Tirad Pass. With the aide of a spy, Jose Galut, He revealed a secret approach to the Americans. This caused the defeat of the troops of Gregorio del Pilar.

He died in the Battle of Tirad Pass where he was fighting against Texas Regiment and Infantry Regiment. An American officer, Lt. Dennis P. Quinlan ordered his men to give honor to the fallen but valorous foe. Likewise, the National Historical Institute and his town mates in Bulacan also gave him the highest recognitions.