Who is Ben Cortman from I Am Legend and what is their importance?

Ben Cortman, once Robert's neighbor, friend, and co-worker, has been transformed by the vampire bacterium into a vampire who reminds Robert of a "roly poly Oliver Hardy" who has survived shootings, knifings, rock throwing, and other assaults. He is now Robert's chief nemesis and the only vampire (except for Ruth) who is named in the book. During the day, Ben sleeps in a coma, but at night, he stands outside Robert's house and dares him to come out. On the day that Robert is assaulted en masse, he shoots Ben three times, but Ben survives the attacks. After a while, Ben and Robert settle into a kind of routine in which each keeps up the chase as a kind of game that goes on indefinitely, and Robert never tries to kill him again. Witnessing Ben's brutal slaughter by the mutant vampires is traumatic for Robert, who breaks into tears; he regards Ben's death as "the death of all comedy and all laughter."