This chapter explores the evolutionary complexification of eukaryotic agency, emphasizing the remarkable behavioral and structural innovations in protists. Protists leveraged mechanisms developed during eukaryogenesis to exploit their larger cell size, leading to advanced motility, sensory systems, and environmental adaptability. These innovations enabled them to diversify and thrive across a wide range of ecological niches, innovations that in some branches have developed early complex forms of agency. The chapter also examines the limitations and potential of multicellular protists, highlighting how motility-based agency has driven greater complexification compared to secretion-based strategies. Insights into the transition toward multicellularity provide a foundation for understanding the evolution of further complex manifestations of agency.