Frank Castle was serving in the United States Marine Corps during the Vietnam War for a couple of years until he went on leave to go home to his family in New York. One day he took his wife Maria, daughter Lisa and son Frank Jr. to Central Park for a picnic but coincidentally, the family happened upon the scene of a mob hit. Fearing witnesses, the mobsters murdered Castle's family in cold blood and escaped. As he cradled their bodies while screaming in horror, he made a vow to himself that he would take vengeance upon those who killed his family, by becoming the vigilante known as the Punisher.
Even with his efforts, the United States and it's society fell to chaos and disorder. Later on Castle was taken captive by Iron Man and his secret group known as the Illuminati to convince him the only way to bring hope back to the people was to make Castle into the new Captain America. Injected with a newly modified version of the Super-Soldier serum created by Mister Fantastic, Castle's physiology changed making him stronger, faster, more powerful than Steve Rogers ever was. Given the uniform and the shield, Frank quickly took on the role with great pride.
Castle became a member of the Avengers after he proved himself against multiple enemies like the Red Skull and the cosmic being Thanos. Serving as an Avengers member over the years, Frank became disillusioned by Tony Stark's plan to mass produce serum-powered "Captain Americas" to each state for his Captain Americorps initiative. Castle eventually retired and moved back to New York City but his heroism inspired many including a young girl named Ava. He taught her how to throw a shield by using a garbage lid. As she grew older she waited for him to come back but it never happened, but he instilled hope in her where she ended up leading a squad of her own Americorps.