Smeagol- He is also known as Gollum. He is only mentioned by Gandalf in the book until the end where he is mentioned again by Frodo and Samwise. He is following the fellowship in hope that he could steal the ring back from Frodo. He says that it is his birthday present, but you have to read the book to find out the story behind that. Gollum plays a much larger role in The Hobbit, which I recommend you also read.