Throughout the movie, we see a man has been talking to James Cole with a mysterious voice, Cole asked him about his identity, but he denied to express it. Once Cole doubted a beggar in 1996 to be owner of that voice, but later Railley understood he was not that "person". So who was he? And why was he calling Cole "Bob" all the time?
This character is referred to as Louie/Rasping Voice on IMDb, and feelings are mixed on the interpretation of the character.
In the feedback section of the movie's IMDb page, there is a lot of discussion over the idea that Louie is a fellow time 'volunteer', who has extracted his own teeth to avoid being tracked.
However, other sites, including this one, suggest that Cole might have been hallucinating the entire time and that he has made up the Louie character and the rasping voice in his head.
The reason he was called 'Bob' could be because this is a form of greeting (although the correct pronunciation would be along the lines of "hey, Bub") - however, Cole is called Bob in the future segments, which leads me to believe that he was being mistaken for a different volunteer.
Here is a sample of dialogue that coroborates the fellow traveler theory: