Heelksha
From The Stargate Omnipedia
Evil gods to the people of the Land of Light (likely the Goa'uld). The heelksha had not been through the gate for some time, and it was long-past due for them to return.
KEY EPISODE
The Broca Divide - SG-1 travels to the Land of Light and learns of an evil force who bring about a mysterious illness in the Land of the Dark.