The Punisher (aka Frank Castle/ Francis Castiglione) was created by writer Gerry Conway and artist John Romita, Sr, and made his debut in The Amazing Spider-Man #129 back in 1974.
When he first appeared on the comic book, the Punisher was initially an antagonist of Spider-Man. He is portrayed as a bloodthirsty vigilante who has no qualms about killing gangsters, something that most superheroes of that time refrained from doing.
Frank Castle was illustrated to be one who was driven by the grief from the deaths of his wife and two children, who were killed by the mob for witnessing a killing in New York City's Central Park, he took on the role as a "Punisher" to wage a one-man war on the mob and all criminals in general by using all manner of conventional war weaponry. His family's killers were the first to be slain. A war veteran of the U.S. Marine Corps, Castle is a master of martial arts, stealth tactics, guerrilla warfare, and a wide variety of weapons.
While a Marine, he also received training from the Airborne School and U.S. Navy SEALs as well as cross-training with the Australian Special Air Service Regiment during the Vietnam War. In addition, since beginning his work as the Punisher, Castle has expand his skills in areas that aid in his mission, such as disguise, acting, use of non-military weapons, etc.
Also, he is trained in various forms of camouflage and stealth. He is also highly adept at hand-to-hand combat, and has been trained in multiple forms of martial arts such as Nash Ryu Jujutsu, Ninjutsu, Shorin-ryu Karate, Hwa Rang Do, and Chin Na.
The old war dog is also high in pain tolerance, as complimented by Nick Fury and Tony Stark. And because of his trainings, also has complete control of his mind and consciousness, providing a strong resistance against psychic and telepathic powers that are used against him.
The Punisher remains high in popularity among readers, since his first appearance, probably due to his "powers" which are closer to reality. Almost every single part of his mastery of weapons to martial arts could be managed by an average Joe through sheer hardwork and determination. Easily related to, plus his passion for his work make him the man for many boys and men.
After all, how many men could say "It doesn't feel different from any other day", when some mind-controlling female villians were making an attempt on him.