Ernest Medina was born on August 27, 1936 and grew up in a small town called Springer, New Mexico in a Mexican-American family. Since before he graduated high school, Medina spent most of his life in the military. He lied about his age in order to join the National Guard at 16 years old. He served for only a few years in the National Guard before leaving the military and working in the civilian world. He enlisted in the Army in 1956, deployed to places such as Germany, came back to the US to attend Officer Candidate School (OCS) where he graduated 4th in his class, and was deployed to Hawaii in preparation for the war in Vietnam. While there, Cpt Medina was assigned to lead Charlie Company. He thoroughly trained them in order to prepare for the extreme swampy conditions that they would soon encounter in Vietnam.
Charlie Company was deployed to Vietnam in 1968. Before the My Lai incident, Medina had a great deal of respect from Charlie Company as a feared leader. During the My Lai Massacre, Medina commanded his company to destroy the village, killing everyone in it. They had been informed the 148th Vietcong infantry battalion was being housed there. However, Medina and Calley did not repeal that command even after it was apparent that they were killing innocent civilians, not Vietcong soldiers. He was later court-martialed for his actions but the charges were acquitted. Due to these charges, he was ultimately denied his promotion to major.
He decided to leave the military without ever speaking publicly about the event and moved to Michigan to work in a helicopter manufacturing company.