particle
sentence-ending particle adding force; used for emphasis or command
Primarily used in masculine speech at the end of a sentence to add force, assertiveness, or to indicate a command. Often heard in casual or rough male conversation.
行くぞ！
Let's go! / I'm going!
やるぞ！
I'll do it!
静かにしろって言ったぞ。
I told you to be quiet!
The exact origin is uncertain, but it is a native Japanese particle that has been used historically in masculine, assertive speech.