The Mask of Anubis was a personal forcefield used by the System Lord Anubis. Anubis utilized this forcefield to make his immaterial half-ascended form look Human. The shield's origin was unknown, though it was possible that Anubis designed it himself after his fall from ascension or that it was an artifact of the Ancients. It has the appearance of the event horizon of an active Stargate.
Anubis was first seen using this forcefield when he captured the Asgard Thor. Anubis continued using this forcefield until it was destroyed in the Battle of Antarctica. After his escape off the planet Earth he didn't recreate his forcefield but instead used hosts who eventually died.