The term 'Mysterious Character' can be summarized as a character who is shrouded in mystery. This could refer to a character in a book, movie, or television show who is not fully understood by the audience, or it could refer to a real-life person whose identity and motives are unknown. The crossword solution for this term is 'RUNE, ' which is a type of symbol that was used in ancient cultures to convey messages or invoke magical powers. Runes were often used to represent mysterious concepts, making them a fitting solution for this term.