This paper focuses on deriving power-system linear models directly from collected PMU data with the aim of feeding a wide-area damping controller (WADC) architecture. To this end, a data-assisted dominant modal realization in state space is derived from frequency-response data, impulse-response data, and the retained impulse dynamic subspace, enabling WADC synthesis without requiring a full phenomenological network model. Then, a discrete-time linear quadratic Gaussian (LQG) structure is synthesized on the identified dominant modal realization, combining damping action with reconstruction of reduced states from WAMS measurements. Finally, the symbiosis between the proposed realization and the controller is validated on the Kundur and New England–New York power networks by using modal displacement and nonlinear post-fault simulations, demonstrating coordinated damping through selected AVR supplementary inputs.