The Space-Spawn were an alien race born in the heart of a burning star. They are one of three major races involved in an intergalactic war (the second being the N'Kai). Nokkar believed the gargoyle Avalon travellers (Goliath, Angela, and Bronx) were extraterrestrial minions of the Space-Spawn, though he was later corrected.
Greg Weisman's Master Plan
In 2198, the Space-Spawn are due to invade and kidnap numerous world leaders and conquer Earth, leading to the events of the proposed Gargoyles 2198 series.
Various fan interpretations of the little-detailed Space-Spawn have included Cthulhu-like abominations and tall gargoyle-like humanoids. None of these interpretations seem likely, however.