Please find a movie name

I forgot what it was called, but the ending made me wonder endlessly: a character who could disguise himself into any appearance, blowing his signature whistle as the curtain fell. He had thought that everything was over before this, but it felt like it had just begun. The ending of the movie seems to be Black Eyed Peas's boom boom poof, but I've searched, only the special forces use this song. But that didn't seem to be the case. Does anyone know about this movie?