Luther Alexander is the first character you meet in the game as part of the Introduction, where he introduces you to actions and how they work throughout the game.
Luther works at So Chic in Downtown LA as your manager. After completing the Take Miami goal, you will stop working at So Chic and Luther will appear to be irritated whenever you visit the boutique, mainly due to your resignation.
Later in the game, you will be able to purchase So Chic. Even as the owner, you can still earn Cash through working a shift by speaking to Luther, who will treat you more nicely. You can also ask him for advice regarding the game.