The term 'PART OF A SPLIT PERSONALITY' can be solved by the crossword clue 'JEKYLL' (6 letters). Jekyll is a character from Robert Louis Stevenson's 1886 novella Strange Case of Dr. Jekyll and Mr. Hyde. He is a doctor who creates a potion that transforms him into his evil alter ego, Mr. Hyde. Jekyll is thus part of a split personality, with his good side being represented by Jekyll and his evil side being represented by Hyde.