A key issue in cosmology is the formation of massive (>L*), early type galaxies. To reconcile their predominant old stellar populations and the uniformity in physical properties with the hierarchical buildup of structures within the LCDM framwork, poorly understood processes such as feedback (interaction between galaxies and their immediate environment via e.g. radio outflows) and "dry" mergers (mergers involving gas-poor galactic systems) have been invoked in leading galaxy formation theories. I will discuss the roles of mergers and feedback in shaping the massive galaxy populations, using galaxies that reside in groups and clusters. In the first half of the talk the importance of mergers will be assessed with the cluster galaxy luminosity function and scaling relations. In the second half I will focus on the physical properties of the radio-loud AGNs in the local Universe, and present a model for the evolution of powerful radio galaxies that can account for the source counts from 0.15 GHz to 150 GHz, and radio luminosity function out to z~2.

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