Who is Gavin Verheek from The Pelican Brief and what is their importance?

Gavin Verheek is one of Thomas Callahan's best friends at the Georgetown law school 20 years previously, Verheek drops out of lucrative private practice to work for the FBI as Special Counsel to the Director, F. Denton Voyles. Verheek is overwhelmed with work following the assassination of Supreme Court justices Rosenberg and Jensen, but the friends meet while Callahan is in DC. Verheek can divulge nothing and wants to talk about Callahan's latest young lover. He is on his third wife, who is worth about $5 million but is neurotic and depressed.