The Unified Model of Active Galactic Nuclei (UMAGN) serves as a comprehensive theoretical framework designed to elucidate the myriad observations of AGN, encompassing both quasars and Seyfert galaxies. This model attributes observed variations to distinct orientations of a circumnuclear matter disk around a supermassive black hole (SMBH). The primary factor influencing the observational diversity lies in the alignment of the AGN with the observer's line of sight. We provide an exhaustive overview of observational evidence, empirical and theoretical research, tracing pivotal milestones that have led to a unified perspective. Our exposition encapsulates the scientific journey culminating in the proposal of UMAGN, delving into insights regarding the accretion disk, torus, and relativistic jet. We emphasize key properties of objects within the UMAGN framework. Furthermore, we underscore rece...