close the gates

I never understood this character in super mario
who is he?
and what does he do?

Kamek. Bowser’s Right hand man.

thanks for answering me
does kamek repair browser's castle or what?

He casts curses on people.

If you play or watch NSMB, Kamek shows up during many boss intros and changes the arena or gives the boss a new ability to add a “twist” to the fight. He even has his own boss fight in the last tower level in NSMBU, or New Super Mario Bros-U.