This chapter explores the role of virtual agents in immersive fashion retail, distinguishing between embodied agents—digital self-representations controlled by the user—and autonomous agents, such as NPCs, which operate as social actors within XR environments. Embodied agents enable users to interact with VEs through body-mapped avatars that support VTO experiences and identity expression. Drawing on embodiment theory and interaction design, the chapter examines how visual fidelity, sensory feedback, and real-time motor synchronization enhance presence, usability, and purchase intention. In contrast, autonomous agents function as virtual sales assistants or co-shoppers, contributing to perceived realism, emotional engagement, and brand interaction. Key design dimensions across both agent types include viewpoint, sensory cues, anthropomorphism, and interactivity. A comparative analysis of recent XR retail studies demonstrates how the design of virtual agents influences user behavior, satisfaction, and trust. The chapter proposes a structured framework for designing both embodied and autonomous agents, grounded in empirical evidence and translated into actionable design insights. It also addresses key challenges, such as limited avatar diversity, the absence of haptic feedback, and the need for more natural, multimodal interaction paradigms.