Luke Skywalker's mentor is Yoda, a legendary Jedi Master and powerful Force user. He first appeared in the 1980 film 'The Empire Strikes Back' and has since become one of the most iconic characters in the Star Wars franchise. Yoda is known for his wisdom, wit, and sage advice, which he imparts to Luke during their time together. Yoda is also known for his unique speech pattern, which often involves inverting the syntax of his sentences.