Tobe is Miss Emily's manservant. He is similar to a butler because he opens the door to "guests" and lives in the Grierson house.
Because "A Rose for Emily" heavily discusses the conflict between tradition (especially traditions of the Old South) and more modern thinking, Faulkner uses Tobe as one of the elements of the town's "traditions." The author refers to him most often as "the Negro" instead by name, implying that Miss Emily and even other members of the town have not eliminated their problems with discrimination and the dehumanization of other races. One might expect this of Miss Emily because she is eccentric and obviously living in the past, but the narrator of the story, who is a member of the town, also chooses to refer to Tobe by the term more often than by his proper name.
Likewise, Tobe represents the barrier between not only blacks and whites during the time but also between old and new ways of thinking. He continues to work for Miss Emily, possibly when she can no longer pay him. Faulkner does not give a reason for Tobe's loyalty, but it seems that Tobe possesses a protective attitude toward Emily Grierson. He keeps her secret for many years and even stays around after she has died, but only long enough to let "visitors" into his dead employer's house. Then he
"walk[s] right through the house and out the back and was not seen again."
His action is his last "duty" for Emily. He could have stayed behind to watch the townspeople's reaction to her room, but it is almost as if he wants to know nothing of their gossip and likely criticism of her. He would not think of himself as her friend because his and her sense of tradition dictated otherwise, but it also influences him to practice loyalty toward someone who had for so long been a part of his life. Even his exit (through the back door) implies that tradition has been so deeply ingrained in him that he does not know how to act apart from it.
Tobe is Miss Emily's black manservant. It is historically important to understand that he was probably owned by her family, or perhaps his family was owned by hers, even if he was a free man. Either way, he stayed with her until the end, and when she was dead, only then did he bolt as quickly as he could. His role includes being the male companion to Miss Emily in a world devoid of men...her father died, her suitors disappeared, and then Homer met his unfortunate end. In Miss Emily's world, it would have been very inappropriate for a female of any age to travel alone without the escort of a male companion. Most of the time this would have been a father, brother, or husband, but in a pinch, a male servant will do just fine. Tobe, I am sure, served her well and saw many things he probably wished he didn't. He didn't stay long enough to explain anything to anyone after Miss Emily's death.