Who is Francois Monserrat from Black Friday and what is their importance?

Francois Monserrat is an elusive person some officials believe does not really exist but is actually the combined identity of several people. David believes that Isabella Marqueza was Monserrat's lover, but she says that she's never seen him, that he is also searching for Green Band and that he doesn't understand what's happening either. Monserrat, convinced that she revealed something about him, kills Isabella. Several people say they know Monserrat by a different name because they've seen him on television and in the newspapers. As it turns out, Monserrat is FBI Director Walter Trentkamp.