Libby - Libby is a character whose background has never really fully been shown to us. She was a member of the tailies and upon meeting up with the losties, found a connection with Hurley. We learn later that she spent time in Santa Ana while Hurley was there and gave Desmond the boat that eventually crashed on the island. She was murdered by Michael while he was freeing Ben.
vs.
Charlotte Lewis Staples - Charlotte is an anthropologist hired by Widmore to take a Freighter to the island. Charlotte as it turned out, was actually looking for her birthplace. It turns out, she was a member of the DI as a child and was taken away from the island at a young age. She would end up time tripping on the island with Sawyer, Juliet, Miles, Jin and Daniel. Charlotte died before Locke was able to stop the time shifting.
