The Punisher
In short
Frank Castle is a Marvel Comics antihero who uses lethal force to wage a private war against organised crime. He first appeared in The Amazing Spider-Man #129 in 1974.
In plain words
He is a former soldier who became a vigilante after his family was killed by criminals. Unlike traditional superheroes, he does not arrest criminals but kills them instead.
A simple example
If a gang is terrorising a neighbourhood, The Punisher would use weapons and combat training to eliminate the gang members permanently rather than calling the police.
Why it matters
The character explores the moral grey areas of justice and vigilantism. He remains a popular figure because he challenges the standard rules of the superhero genre.
Easy to mix up
Do not confuse him with Batman, who is a hero that strictly avoids killing his enemies.