Great Kanohi are powerful masks that are most often worn by Toa heroes, although they can also be used by some other species with time, effort, and training.  The abilities that these masks grant to their wearers can be significant enough to turn the tides of battle, and as a result they can be difficult to find compared to their Noble counterparts.  Masks may also be fashioned in these shapes out of respect for figures of legend, or simply to lend their bearers an air of valor.