  The Unified Model of Active Galactic Nuclei (UMAGN) is a comprehensive
theoretical framework aimed at elucidating the diverse observations of AGN,
encompassing quasars and Seyfert galaxies. The Model attributes the observed
variations to different orientations of a surrounding matter disk around a
supermassive black hole (SMBH), with the primary factor influencing
observational diversity being the alignment of the AGN with the observer's line
of sight. We present a comprehensive overview of the observational evidence,
empirical and theoretical research, tracing key milestones that led to a
unified perspective. We encapsulate the scientific journey culminating in the
proposal of the UMAGN, including insights into the accretion disk, torus, and
relativistic jet, and emphasize the properties of objects within UMAGN.
Additionally, we underscore recent progress in multimessenger research
involving electromagnetic waves, gravitational waves, astroparticles, and
neutrinos, notably through collaborations such as the Event Horizon Telescope,
LIGO/Virgo, IceCube, Pierre Auger, and KM3Net. We argue that these advancements
present opportunities to enhance and refine UMAGN, contributing to a deeper
understanding of AGNs and their implications for the formation and evolution of
galaxies. The convergence of observational and theoretical research, coupled
with emerging multimessenger techniques, paves the way for further strides in
comprehending these enigmatic cosmic phenomena.
