Creep is derived from the Old English root that mean to move or walk with the body close to the ground and is related to the term "cripple."
The history of the slang use of the term word "creep" seems to date back to around 1860 to describe the sensation of feeling non-present creatures crawling over ones skin.
Creep began being used to describe a person during the 1930's and meant roughly the same thing as a similar slang terms like a drip or goon, but on a drip or goon that gives you the shivers.
Morris, William and Mary. Dictionary of Word and Phrase Origins