plagiarist

One who plagiarizes, or purloins the words, writings, or ideas of another, and passes them off as his own; a literary thief; a plagiary.

noun

One who illicitly reproduces the artistic work, for example, of another: cribber, pirate, plagiarizer. See give/take/reciprocity, words.

The noun has one meaning:

Meaning #1: someone who uses another person's words or ideas as if they were his own
  Synonyms: plagiarizer, plagiariser, literary pirate, pirate