Which of the following Marvel characters fought in the Vietnam War?

The Punisher (real name Frank Castle, Sr.) is a violent vigilante from Marvel comics and varies from being a dark anti-hero to being an outright protagonist villain depending on the immediate fact situation facing Frank (Punisher).

Francis David "Frank" Castle, Sr., is a former United States Marine-turned-vigilante. Initially, he was depicted as a veteran of the Vietnam War. With updates and alternately, he has had military duty in the fictional Siancong War and the Iraq War. He was a military scout/sniper. He was also skilled in hand-to-hand combat, guerrilla warfare, and skilled marksmanship.

Castle (Punisher) is well known by his skull motif on his chest, originally envisioned by his creators as a skull-and-crossbones symbol on his right breast. Following the widespread appropriation of this logo by the Blue Lives Matter movement, it was officially retired from active use by Marvel Entertainment in 2022. It was replaced by a new horned-skull motif inspired by the Japanese mythological demon Oni.

The Punisher was born in the Hell's Kitchen district of New York City. According to him, his parents were too old when they had him and consequently had difficulties trying to control him. He was also a trouble-maker when he was a young man, with a strong desire to hurt people, which he would later claim that he often did, quickly becoming a highly effective fighter. Castle also played baseball, and his father attended all of his games.