Powerful extragalactic radio sources are characterised by kpc-scale synchrotron emission associated with highly-collimated outflows of relativistic plasma. It is hypothesized that this outflowing plasma is powered by accretion processes concomitant with a central massive black hole. The radio morphologies of these sources comprise jets, lobes and for the most powerful sources, hotspots. At first sight, powerful extragalactic radio sources are a mixed group of objects, with the result that only some gross property delineates them further (e.g. steep-spectrum or flat-spectrum). However, there is accumulating observational evidence which suggests that it is the orientation of the radio axis to our line-of-sight which dictates their observed characteristics. This orientation-dependence has been incorporated into `unified schemes', which physically-link apparently disparate radio source types via the random orientation of a `parent' population on the plane of the sky. This paper summarises the `dual-population unified scheme' paradigm investigated by and discusses some of its implications with respect to radio source cosmology.