Grell is a sandworm species from the planet Kerona (original version) in the Space Quest I: The Sarien Encounter (original version) time sector.
Background
Grell appears to be the given name for an individual annelid sandworm on the planet Kerona, the specific sandworm that lives near the Desert Cliffs and the Dunes of Ulence. It is feared both in the Keronian underground settlement and Ulence Flats.
Grell and his like dwell in caves below the sand. If one stands on the surface too long they have a chance becoming a rare moist meal for him. Skimmers on Kerona hover approximately 1/2 meter above the traveling surface. This is very important because of Grell. The average Keronian appears to refer to its kind (and a later new variety) as the sandworms of Kerona.[1]
Murderers and muggers may use Grell to get rid of their victims, turning them into Grell kibble. [2]
Deadbeats and thieves may also be fed to Grell as punishment for attempting to cheat or steal from Ulence Flat's businesses.[3]
It would appear after Roger Wilco's time travel another species of Grell (a reptilian species) was unleashed on the planet in even greater numbers (as well as an extinct Grell species they may have evolved from) in the Space Quest I: Roger Wilco in the Sarien Encounter (time sector).
Physiology and traits
The annelid Keronian sandworms have at two eyes one on each side of its head segment (or one eye on one side of its head segement). It's maw is made up four segmented jaws, which the sandworm waits patiently for a victim to walk over, before rising up exposing its eyes (or eye) and snapping them closed (perhaps not unlike a sand lion of earth). It then pulls back underground, leaving only the disrupted service to show of its passing.
The maw of the annelid Grell is similar to that of the Estrosian Sea Slug.
Behind the scenes
The reference to the Grell as a singular named individual of its species, appears to be a reference to the Sarlacc of Star Wars lore. Infact the idea that criminals and others would feed their victims to "The Grell" also appears to be further references linking the Grell to the ideas surrounding the Sarlacc.
The grell in SQ1AGI looks to be the cross between a worm and a squid with a mouth that opens in four directions..