Angle dependent obscuration by a thick dusty torus "unifies" Broad and Narrow line AGN. The central continuum and broad line region are only visible when viewed close (~50o) to the polar axis. [Figure from Peterson's AGN book.]
In addition to angle dependent obscuration, for radio loud AGN (i.e. those with a powerful jet) Doppler boosting renders the jet and nuclear radio emission angle dependent, giving rise to Core Dominated and Lobe Dominated radio sources. Viewing right down the jet axis in which both radio and optical emission are boosted gives a BL Lac object (galaxy and emission lines drowned out by a featureless continuum). [Figure from Kembhavi & Narlikar's AGN book.]