The study challenges the foundational axiom of consumer theory that the agent holding purchasing power is identical to the agent forming preferences. We introduce the Proxy-Influence Consumer (PIC), an agent with zero budget authority who systematically shapes the preferences of a Budget-Constrained Principal Consumer (BCPC). Formalizing this via a Delegated Utility Function (DUF), we derive new equilibrium conditions, the Influence Elasticity of Demand (IED), and prove that Slutsky symmetry and the Weak Axiom of Revealed Preference fail under PIC influence. Applications to fast-moving consumer goods markets rationalize child-directed advertising strategies and motivate a new welfare measure, Delegated Preference Distortion.