Studying the cold neutral hydrogen (HI) gas in radio galaxies provides an excellent way of investigating both the formation history of the host galaxy and feeding/feedback processes of the AGN. In a comprehensive ongoing study of mapping the HI emission-line gas in nearby radio galaxies, we find that there appear fundamental differences in the large-scale HI properties of different types of radio galaxies (HI-deficient early-type galaxies for FR-I sources, HI-rich merger-systems for FR-IIs and, puzzling, enormous but old HI disks for compact radio sources). This likely implies that the various types of radio galaxies experienced a different formation history, which may be linked to a fundamentally different triggering mechanism of their radio-loud AGN. With current day telescopes we can observe HI only in small samples of the nearest radio galaxies (due to their sparse distribution), but these studies will provide exciting science cases for already planned continuum and HI surveys with upcoming radio telescopes.