Who is Ruth from I Am Legend and what is their importance?

Ruth is a young woman whose two children died in the vampire plague and whose husband was killed by Robert. She is one of an emerging race of mutant vampires who is sent to spy on Robert and obtain the knowledge he has gained about vampires. She tells Robert that her husband was killed by a vampire to gain his sympathy and trust. Although Robert intuitively distrusts her, Robert is genuinely misled by the fact that Ruth is not affected by sunlight, her skin is tanned, and she wears a cross around her neck. These things are explained by the fact that the mutants have devised a pill that will allow them to function briefly during the day, Ruth uses cosmetics to give her a fake tan and apparently does not fear the cross because her mind is not as easily taken in as the earlier breed of vampires. She does, however, become ill when Robert shoves garlic under her nose, which Ruth attributes to a weak stomach and not eating for a week. After completing her spy mission, Ruth and Robert make love, and afterwards she tells Robert she loves him and that he should leave his house. Robert doesn't believe her when she says that she loves him.