This paper introduces a formal framework for modeling observer-dependent collapse dynamics and temporal identity drift within artificial and mathematical systems, grounded entirely in the symbolic foundations of Alpay Algebra. Building upon the fixed-point emergence structures developed in Alpay Algebra I and II, this third installment formalizes the observer-coupled {\phi}-collapse process through transfinite categorical flows and curvature-driven identity operators. We define a novel temporal drift mechanism as a recursive deformation of identity signatures under entangled observer influence, constructing categorical invariants that evolve across fold iterations. The proposed system surpasses conventional identity modeling in explainable AI (XAI) by encoding internal transformation history into a symbolic fixed-point structure, offering provable traceability and temporal coherence. Applications range from AI self-awareness architectures to formal logic systems where identity is not static but dynamically induced by observation. The theoretical results also offer a mathematically rigorous basis for future AI systems with stable self-referential behavior, positioning Alpay Algebra as a next-generation symbolic framework bridging category theory, identity logic, and observer dynamics.