Who is Guy Banister from Libra and what is their importance?

Guy Banister is an ex-FBI agent who has become a private investigator in New Orleans. Banister was one of the agents at the capture of John Dillinger, a story he often tells when he is drunk. Banister was also damaged by the failed invasion at the Bay of Pigs and has become an outspoken opponent to Fidel Castro. It is Banister that T-Jay turns to when Win Everett first outlines his plan. Banister not only gives T-Jay weapons, but he draws Oswald in just when it looks like he was trying to fall off the radar.