Hannibal Lecter is fiction. He's a character in books by the author Thomas Harris. He was introduced in the book "Red Dragon", and then was popularized in "Silence of the Lambs". He was then written about in "Hannibal", and "Hannibal Rising". (Which is the story of his youth and how he became a maniac.)
http://en.wikipedia.org/wiki/Hannibal_Lecter
"Buffalo Bill" was the nickname given to another (fictional) killer in the book "Silence of the Lambs", so that might be what you're thinking of in terms of serial killers. There WAS a real "Buffalo Bill", but he wasn't a serial killer...he was a very famous figure from the Old West.
REAL Buffalo Bill: http://en.wikipedia.org/wiki/Buffalo_Bill
FICTIONAL "Buffalo Bill": http://en.wikipedia.org/wiki/Buffalo_Bill_(The_Silence_of_the_Lambs)
Ed Gein was a real killer, who's unusual traits and ways of dealing with dead bodies was an inspiration behind many fictional serial killers, including Norman Bates in "Psycho", Buffalo Bill in "Silence of the Lambs", and the killers in "The Texas Chainsaw Massacre" He had an obsessive relationship with his mother (inspiration behind "Psycho"), and other than killing, he would dig up dead bodies, and cut them up and use the body parts. He would remove the breasts and sexual organs of women, and wear them like clothes. (Inspiration for "Buffalo Bill" in "Silence of the Lambs".)
http://www.crimelibrary.com/serial_killers/notorious/gein/bill_1.html