Who is Greg Hale from Digital Fortress and what is their importance?

Greg Hale is a former Marine who was immediately discharged from duty when he killed a fellow Marine in a drunken brawl. After exposing the back door that Strathmore had created in the Skipjack program, the NSA hired Greg Hale believed that it would be better to have him on the inside working for them, rather than on the outside working against them.

When Susan uncovers what she believes is email correspondence between Hale and Tankado, she immediately assumes he is Tankado's partner. Not considered a trustworthy person by his fellow coworkers, Hale's innocence in the story is an ironic twist.